to destroy mines you need a whole bunch of scouts and maybe Flak frigs or carriers with fighters.
it is alot of mirco... on the other hand if you want to blast a hole for you fleet to jump in. just send a bunch of scouts plus flak frigs along your route to suicide and clear the way for you.
with the refineries, you should place them next to Un-Colonisable Gravity Wells (UCGW's) with neutral extractors and also in volcanic/ice worlds, to maximise your resource income. other than that, use trade ports and just buy what you dont have
remember that TEC and Vasari refineries will refine resources from neighboring GW's, so you dont have to build 3/4 in every gw, if you have 2 volcanic worlds, for instance, right next to each other, you can build lets say 2 refineries in each well and they bounce off each other so you can build other structures in each GW, that way you dont waste money on refineries you dont use