I dont know who would think doing a custom kit is fun, personally I think it's a big PITA. If you can do ALL of the work your self then it should be no problem. By your own work, I mean your own welding, install, tuning, etc etc.

Right now I've got all the basics: intercooler and piping, turbo, manifold, wastegate, and a DP. But gathering all the bits and pieces to make up the rest of the kit is somewhat of a pain.

There are plenty of places you can go to get your own piping and flanges, so that you can make your own IC piping and DP and exhaust. You can also get a lot of quality components (BOV, WG, manifold) for low price if you look around for used parts, but you run the risk of getting scammed. If you're gonna buy used parts I'd recommend buying from someone in your local area, so you can see what it is you are buying (pick it up yourself).

Before I install the turbo, I plan on getting a new DP made up that starts out as 2.5" but flares out to 3" . But in order to make up a new DP, I need to install the turbo and manifold. Once that's done I make the DP, and the rest of the exhaust. If I knew how to weld I could do it all myself at my local hobby shop, but since I dont know how I have to get it done at a shop.