Research , research , research. And don't settle for cheap knock-offs that you will eventually just replace anyway. In this hobby, you get what you pay for, usually! (there are some exceptions of cheap = good lol) I know Dave on here just sold an upgraded 29g cube, but it seems the buyer bailed on some of the parts and only took the tank and stand. Too bad you didn't walk by that store a week earlier, you could have landed an entire set up for a fraction of the cost... He still might have some of the upgrades available, check with DAS212 and it might save you some money. Dave spares no expense on quality and keeps it well maintained.
First determine what it is you want to keep in the tank and that will help you determine what all you will need to run it, such as lighting, filtration, etc. Good husbandry is the key to success in this hobby, although having the right set up goes a very, very long way!! You want to keep every piece you add to the system as low maintenance as possible, because a year or so down the road you might get burned out if it is too tedious to keep up with, so keep that in mind when choosing equipment!!
One last thing, not all LFS's are equal and I'm sure there are plenty who wouldn't sell you something you don't necessarily need.... BUT, do your homework before you walk in a LFS for equipment. It will save you frustration and money. I try my best to support any LFS that goes that extra mile and is trustworthy, and I recommend everyone support locals, but just be careful what you ask them lol. They are, after all, in the business to sell you stuff! (some that you may not need or want lol)
Oh and BTW, welcome to the best hobby known to man!!! (and CR!)