1) anavar and primo are the least suppressive to HPTA, you will also retain most of the gains you make from them.
2) You can retain your gains from any AAS as long as you use proper PCT, keep training properly and eating right post cycle. However, you must distinguish between what some people incorrectly consider gains and what are truly gains. Test, dbol, drol, and deca will all make you retain water, and hence you'll put on more weight during a cycle with these substances...you will also lose this water weight when you come off. Some idiots will say "you don't keep any of the gains off of dbol and test". Well stupid, thats because water weight is never truly gains to begin with.
With substances like trenbolone, winstrol, primo, anavar, equipoise and masteron, it is more like what you see is what you get. These drugs cause little or no water retention, and therefore when you come off the cycle you don't lose as drastic of an amount of weight. This does not meant they're better than test or the other substances (TEST IS KING) and they will NOT give you better gains. Even with the water weight gone, the true gains you make from test will still surpass any non-aromatizing drug.
3) Steroids will not make your pecker bigger. In fact, they'll make it look even smaller the bigger you get. Only witch-doctors, shamans, practitioners of voodoo and Jahova's Witnesses can make your penis grow larger (they know magic). I would suggest consulting with one of these people if you want a bigger schlong.