There are several things you mentioned that are troublesome.
First, STAY AWAY FROM FM MODULATORS.
There aren't any good FM receivers for a carputer, well, nothing spectacular, and cheap. So far, the HQCT is the closes, and it is about 150 bucks.
TV is also gonna be problematic. There are issues with antennas, and software support. I believe RR has some built in support for some TV cards, but rarely see anyone installing TV on thier carputers, and there is a reason why, it just aint that good.
If you are considering having someone else install the carputer and audio equipment for you, then this whole thing probably isn't for you. Just buy some premade carputer, and a commercial front end, and then have it installed. Truthfully, if a shop needs direction on how to install a carputer, they probably aren't that good of a shop. Carputers are connected to the car the same as any other car audio device, power, ground and accessory. The only addition are the video cable (they do install pimped out TV in cars, right) and perhaps a TS cable. If you want it cheap, you have to do it yourself, and even then, carputers are just NOT CHEAP. You seem to have bitten off more then you can chew.
No one here can decide what is better for you. You have to decide how much you can do yourself, and how much you can spend. There is certainly enough information here, at VW sites, and on for you to do this on your own. Wether you have the mental aquity (don't take it personally, you probably can do things that I can't, I lack the mental aquity for that stuff) to actually understand and do what is being asked of you is something you need to figure out. If you have been unable to locate the information so far, you really need to keep reading and searching for the answers.
Other then the fact that you want FM and TV, no one knows what else you wish to accomplish with your system. Once you determine that, search for the solutions.