In regards to leaving the back open (in my opinion only) you'll do better to provide ample air intake at the bottom and an escape/exhaust area at the top. (These could both still be in the back.) WHY? Have you ever cleaned dust-bunnies from cabling and from behind components? Once your setup is finalized it'll (hopefully) be a while B-4 you go back there again. It can get to be real mess. Just be sure to leave about 3 to 4 inches clearance in the back so everything can breath.

Patterned front with holes? Hopefully all your equipment and shelving will work in unison to let your IR recievers peek "line-'o-site" at your seating position. (Probably not.) If you leave the front open you won't have IR issues and you won't have to worry much about heat exchange.

MDF has low-resonance but how are you going to finish it? It's hard to get a nice finish on MDF unless you use laminated MDF, and then you have to either buy DIY self-adhesive banding or use an iron to put better quality edge banding on.

After you weigh the cost of materials and your own good labor against the end result you might want to look at a "store-bought" commercially available entertainment center. I have good mid-fi components but I'm doubting they'd sound much different (if any) if I put them in an Oak cabinet or a solid MDF cabinet. Besides a lot of "hardwood" cabinets are veneer laminated over MDF now anyway.

As far as pictures go read some A/V and HT magazines, browse the furniture stores for entertainment centers, and go to a higher end A/V retailer who carries A/V furniture. If you're still bent on building you'll get enough ideas in those places.