If money is not an issue, you can buy stuff new. If you want to save money, you can buy stuff used. It will take a lot more time to get a tank set up from scratch, vs. buying an all-in-one setup. It's true, it is much easier to buy an all-in-one thing, especially if you're not familiar with what kind of equipment you need to buy for it. It's up to you what you choose to do, but if you do go with the setups you linked to, I would go with the one that has T5s. I just think that if you spend that much money on this right now, you won't be happy with it 6 months from now and will have to buy everything all over again...
Anyways, here is what you would need if you wanted to do, say, a tank with a sump.
- display tank
- stand with doors to hide the sump and equipment
- 2 powerheads
- heater
- protein skimmer
- lights (I would go with T5s)
- overflow box
- PVC for plumbing the sump
- return pump to get the water back to the tank
- tank for sump
It seems daunting at first to be able to put all this together yourself. But you do get a great deal of satisfaction from building your tank yourself.
Keep in mind, you say that you are restricted to something that is 30" long at the most... The smaller the tank, the harder it is to keep it maintained and keep your water quality high and your animals alive. If a small tank is not something that you want right now, then perhaps it'd be better to wait until you can get exactly what you want instead of spending hundreds of dollars now, only to have to upgrade within a year and re-spend all that money on a new setup.
Why can't you have a bigger tank? What's up with dad? :)