Same turbos on both kits. If you go stage 1 for quicker spooling turbos (a little) but decide in the future that want more power you can upgrade to the .86 housing that comes with the stage 2 (aprox $200-$250 each). GTM has pushed over 580rwhp on stage 1 turbos (.64 housing)
I would (and in fact will) go stage 1 since I have no plans of pushing more than 500rwhp on a stock block and if I ever decide to build the engine I will then uprgrade housings, or just swap out for bigger turbos.
You can use the stock clutch until it gives out. A 34R oil cooler would be the best option in TX but you can keep the 25R and keep and eye on temps, then decide if you need to upgrade. Fuel system is included with the kit, but you will need to get one step colder spark plugs. Also I agree on going with the 6psi (5.88psi) spring and getting a boost controller. HKS EVC-S can be had for about $350.
Boost and AFR gauges are good ideas so that you can monitor and catch potential problems before they occur.
Just my 2cents