among injectable AAS, deca is probably has the least amount of side-effects in proportion to its mass-building effects. Honestly even for a beginner, 8-9 week cycles with moderate amounts of deca are fine. As for side-effect reduction, here are 2 things I can reccomend: eat good food and and get rest. Also why are you-stacking deca and test? Are you taking both of them at the same time for 12 weeks. BAD IDEA.
You will lose some of the joint-regenerating properties, and some vascularity. Just keep your protein levels up(2.5g./KG of bodyweight), and you should be fine.(Also plan out a PCT, your gonna need one) PM me if you need anymore advice, as I am always willing to help all I can!