Bushmasters in the first or second week will keep them from stretching. It will make them go fat and start maturity. the bushmasters at this point would help more than topping. topping does damage and takes time to recover, not good going into flower
Yes side lighting is always good and will help alot
that space I would just rotate them on the ends and towards the end of flower have the larger ones to the outside smaller in the middle so everyone gets some light.