Although you wont get to see the visual effect masteron has on your physique, it is still worth the effort I believe. It kept my muscles full all the time on minimal carbs. which made me feel jacked all the time. I stopped using it at the end of my cycle to see if I noticed a difference and I definetly did. I will be running about 350mg/week minimum on my next bulk.
as far as your questions go
1) the best effect is the fullness/hardnes
2) No, you still need your anti-e of choice
3) No, masteron is not a muscle builder, it is more of a paritioner.