I do weights and cardio 6am .

I want to incorporate another workout in the PM (6pm), i still have tonnes of energy, and my muscle fatigue is pretty much fully gone by that time.

Can I safely add another workout in the PM? if so.. is it best to do another muscle group? or is working the same ones I did in the AM good?

I am planning a (Tren+Prop) cycle as soon.. so my chances of over taining then will be much less... what are my limitations when on a cycle?