Always be cautious with thick head gaskets, they do lower compression but it also messes up the quench on the heads/piston, which can invite knock problems.
What do you have lined for for fueling? Boosted engines need additional fuel pressure at the injector tip and larger injectors. If the Bosch injectors work the Buick 3800's have 36 lb injectors (at 4 bar), which should support your fueling needs just fine and low cost on injectors. You can find them used easy, I picked up 2 sets for $50 each used. Injectors rarely fail these days and you can have places like
http://witchhunter.com/ clean them and flow them for reasonable cost.
Rules with Turbos:
High flow exhaust (don't let anyone tell you to ADD backpressure for a turbo, they have no idea what they are talking about)
Free flowing intake
Avoid tuned intakes like dual plane (carb style), it can make a turbo engine peaky. You shouldn't have real issues here.
Some sort of knock retard for ping control. Broken pistons suck (ask me how I know....)
Upgraded cooling system. Keep it cool. Stock radiator might not be near enough.
ECU tuning is really needed, not sure how you can do it on a Lexus. But it is needed to be safe.
Be cautious on cutting corners on a tight budget too, you can end up with a pile of parts that is ruined the first time you punch it and something goes lean or it knocks and breaks something.