personally i recomend building a boosted application to handle many different turbo components are variations. such as if you get a gt2871r and larger down the road you want a gt35r if you get the right components that will allow the transition of parts to be seemless and you dont have to completely change up your setup to adapt a turbo or other parts then that will save you down time,money and overall time in the long run.
do you need springs and retainers, i would personally do it, this will save you a step in the future if you decide to go with a stage 1 or 2 that dont require valves and springs but you do it anyway now, it will allow you to go with a larger cam later without hassle and trouble. saving you steps in the process.
valve lift of the camshafts also depend on the need for springs and retainers or not.
another thing to think about is that alot of the time smaller turbos like the gt2871r make very efficent power within the factory rpm range thus not needing a high rev to make efficent power.
on the other hande if you were to want a gt3582r down the road, the 35r is going to be much more top end efficent needing a higher rev limit to expand the spectrum of power made, where as the smaller efficent powers will have a range from 1500 to 7500rpm of power the larger turbos might only be 5500 to 7500 or if you take those extra steps now having the ability to rev higher down the road will help you out in the long run, that extra 7500 to 9000 will make a difference........that is just me tho
im running a 38mm tial wastegate on my setup
i always tell people boosted applications are addicting, you never have enough and theres never enough power, never enough boost, so build accordingly, i dont believe there is ANY turbo setup ive EVER built or EVER seen that was ''overbuilt for turbo'' i dont know many people who build turbo applications to keep them in one specific setup, they are always forever changing, and having taking prior precautions in building the engine to handle anything is best.