Really, all other things being equel, and considering the higher traction tracks we are getting now.
CoG and cenralization of mass are the most important things to consider.
Anytime you can lower the CoG then do it.
I would try and do all the ideas in one go, that way you have more of a chance of actually feeling the results straight away.
You may still get results from lap times too.
Plus, its good fun trying to make the car better then it was b4 !