Well mega dosing bcaa has very little disadvantages (if any at all), but imo mega dosing will be user dependent based on quality of diet and more importantly intensity/duration of training.
I suggest you purchase the or bulk BCAA (or a both and mix them, thats what I personally do) and try them at label directions or just a tad above. When I first started dosing with , I noticed substantial benefits and ensuing muscular strength gains. Start low and adjust your dosing scheme when you become more experienced with its use (this goes for the majority of the products on the market).
As far as other supplements go that again depends on your diet and training experience.