Some people just send off their LS ecu to have the vats (ecu vehicle security) deleted and that's it. It's only 70 bucks or so for that to be done. That keeps you at stock power levels. However good LS specialized tuning shops have performance dyno tuned files of which they have spent significant time on they can flash into the ecu while deleting the vats for additional cost, usually around 200 bucks. The oem tune is very conservative and quite a bit more power can be gained, you should get between 310 to 330hp on a 5.3. Keep in mind the 4.8, 5.3, and 6.0 that are usually swapped are truck engines, so they have cams focused more on torque and not hp like the 6.2 usually is. You can always go bigger LS later, they are all the same dimensions externally, the wiring all plugs in for the most part. The problem with a 6.0 or 6.2 sometimes is if you find a decent deal it will sell quickly. The minimum cost to have a shop do a nice LS swap is around 25k. Diy probably 7k for a emission compliant Ls swap that's well integrated in the cruiser and lots and lots of labor hours. If you've never done a swap b4, the 25k is worth it in my opinion. Another option with a LS swap is to get the engine physically mounted yourself which isn't too terribly hard. Then take it to a shop and have them do the rest. Might shave off a couple grand. This is all what I've only learned from research on my LS so I could be off on some of this.
For the turbo kit, I think wits end is asking 6k or so. What are shops charging in labor hours to install the turbo?