The key is take your time and double and triple check every nut, bolt, line, etc.......
Pump some oil into the turbo oil gallery before firing up the engine.
Do not fire it up until you have a base level tune for your mod level unless a very simple and known mod that does not need a tune or can be used until tuned.
Check all fluid levels, top off as needed.
Start it up and let it warm up while looking and listening to every single thing you touched.
Watch for leaks of any kind.
Shut it down, let it cool, keep looking for leaks, check all fasteners again.
Check all fluid levels again and top off again.
Start it up, let it warm up a bit and take it out but do not get on it, drive around and see how it feels and sounds, anything amiss, shut it down immediately.
Check for leaks again.
OK, then drive it a bit further, get on it a bit, etc.......baby steps are a good thing to do.
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Personal example:
I have a huge list of mods on my car from 293 miles when I started the project and 7 months later took it off the lift for the first drive, worked on tuning, etc and at 1k miles took it for a two day track event and drove the piss out of it to see if any weak links, 200 plus miles off all out and often over driving it on purpose and the only issue was losing 2PSI in one tire.
Track time is expensive, a car breaking on track can be deadly dangerous, being annal about being prepared has a huge payback.
The same applies for any modded street only car.