Custom TV unit build....

i do forsee some problems...

-overly complicated design which is going to be hard to build correctly.
-no space around components which means that they will overheat which is bad.
-no mention of provisions for ventilation
-subwoofer is in the cabinet which could cause issues if its not a front firing type.

what i would do differently..

-use a simpler design for ease of fabrication
-you may want to alter the design and dimensions to fit what plywood sises you can get locally to avoid waste.
-instead of built in shelves, use peg holes or an adjustable shelving strip to make height adjustable shelving.
-instead of using solid wood perhaps use tight weave wire shelving used in closets so air circulates. or, think about cutouts for venting.
-have at least 3 inches (about 75mm) clear area around components at minimum.
-think about having some sort of cooling fans pulling in cool air to certain components on the rear panel.
-if you place your consoles on the far left and far right you can have cents on the side panels to help cool them. (not reflected in picture below)
-some smaller components can be placed next to eachother to fit shelving space.

something like this.. of course you could use more "sections" if you think it will fit your components better. they also do not all have to be the same size. you could for instance have a center wide cabinet for the receiver and wide components, smaller sections for your consoles and then a different sized box for your storage cabinets.

that looks better.

of course the top drawers can be whatever width you want them to be (they dont necessarily need to match the bottom)

remember not to make them too small if you intend to install sliders after the fact since you wont be able to get any tools inside to adjust them. you will also want to make sure the draws work before installing the back. you could always make wood slides though like http/dslides.net/wp-content/uploads/2011/10/drawer-slides.jpg or just have the drawer rest and slide on blocks of wood but this isnt as classy.

as far as how to assemble it..

i would personally suggest a dado joint http/8uzaw1vvi42hi5sw.zippykid.netdna-cdn.com/wp-content/uploads/2011/04/kitchen-cabinets-dado-joint.png which you would cut into the top of the bottom piece, top and bottom of the mid piece and the bottom of the top piece. this would give you a nice strong frame without requiring any brackets since putting screws into the side of plywood doesnt work well.

for the outside corners you might want to double rabbet http/www.table-saw-guide.com/image-files/double-rabbet.jpg the joints and glue them.

the back is typically just a sheet of 1/4" plywood so can be tacked on with finish nails.

if you want a little more rigidity you could use some metal braces in the corners, add some diagnonal bracing or use a thicker sheet of plywood for the back.

for the inside shelving i would suggest using track like this http/www.home-style-choices.com/images/shelf-standard-243x265.jpg since its very easy to do. its quite a bit more work to do and getting it right at home without the right tools is hard but drilling holes for cabinet shelf hangers also works http/www.cabinetsquick.com/images/guide/linebore.jpg but wouldnt be what i would suggest in this case.

i am not sure what you want to put in the drawers. they should be as wide as they need to be to support whatever you will be putting inside them.

if you build the base section first and dont put the top on yet you could work out all the drawer slides rather easily by installing them as you work across putting the drawer verticals in. i would say to go with a wooden slide for ease of construction however yo ucould go with cabinet slides if you dont mind extra work aligning them.

five drawers would be 1.8ft each (550mm) which are wide enough for most common items you would have in such a unit such as games, movies, etc. you could of course get away with as you have it.. smaller drawers if it works for your items. you're going to have to build the bottom first and top last though if you do smaller drawers so that you can work on them. remember... you will lose a bit of width and height on the drawers due to construction as seen below so a bit wider drawer area then what you need would be suggested!

if using .75inch thick (19mm) plywood/boards...
lose on height: thickness of plywood + small gap at the top + small gap at the bottom. estimated 1.5inch loss (38mm)
lose on width: 2x thickness of plywood + 2x thickness of slide. estimated 3inch loss (76mm)

you can see an example of what i'm talking about here although it uses metal slides instead. http/www.idocabinet.com/pic/Side%20Mount%20Self-Closing%20Full%20Extension%20Drawer%20Slide.jpg you not only lose a bit of space for the gaps around the drawer but also for the thickness of the drawer material so your actual useable space is less than the space you put into your frame.

if you look at the "build" link in my signature you can see what i personally use. its a product called panduit and while i'm not sure if that particular brand is available wherever you are... an equivalent likely is. its an industrial cable management option for control panels.having the snap on cover and wires coming out the sides really is quite handy for keeping things nice looking. agreeably the picture of it right now isnt the neatest that i've ever had it and there are more ways to improve it but it works well.

another option would be to install some desk wire frame cable tray behind the cabinet. this works nice, however if it doesnt have a lid some awnry cables tend to push themselves up and out of the tray!

transformers on power supplies are another issue. they do not fit very well into most trays. what i've been doing is to put a few eyehooks screwed into the underside of the desk and zip tying them in place like i did here http/postimg.org/image/5n4p3vup5/ its not pretty but i didnt use panduit or cable tray on this desk... and its 100% better then the rats nest it was.

its also possible to do something like this http/cloudfront-assets.unclutterer.com/wp-content/uploads/120210-wow.jpg but its a bit more work than using tray and requires more zip ties making it a complete pain to undo if you ever want to change things up or clean things out. i would suggest this method for big power transformers and the like but it may not be ideal for cables.

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as for your design above...

- if you plan on going with the 7 drawers i would line the verticals up with the verticals below. this looks nicer and makes it easier to construct. of course if you go with a different number of drawers this will change but tend to keep it symetrical from left to right.

- remove the spacer between wii and wii u. this is not needed.

- you have some strange double-frame lines going on in your drawing for some reason. your cabinet will only be a single thickness as shown in my drawing.

- your drawers will be a bit oversized to the holes.

- if you wanted to make it looks a bit more presentable... you could make a faceplate for the front like http/www.crwoodworking.com/Face%20Frame%20test%20fit.JPG which would go around the whole outside edge, around the doors and around the drawers. it would also go down on the verticals. basically it would go overtop everything but your adjustable shelves this will cause you to lose a bit of space for your drawers but looks alot nicer. here is an example of frameless vs framed http/tonyscustomcabinets.com/yahoo_site_admin/assets/images/frameframeless2.26115832.jpg