2007 Subaru Forester Exhaust

Hi, All. After I thought we were caught up with this car, two problems I need help with. First is the exhaust leak ;appears at the muffler-to-resonator connector. Whole system is really rusty but no visible holes. Put some 'High Heat Red Silicone' as temp fix. Some blew open after week. But not terribly loud anymore. Has anyone used the exhaust system from Rock Auto Parts? Any good? Last long? Price is great but don't want to buy crap system either.
Next is rust spots over the rear wheel wells. I managed to barely get into the area between the well liner and outer fender by using a plastic stringe to put rust converter in there. It seems to have covered what I can and can't see. As it squirted out between joint of fender and bumper. My next question is what kind of paint is on the car? Enamel (2 part?), Laquer, or Urethane(single stage/2 stage)? Where can I get at reasonable cost. Fixed income doesn't allow much leeway. I was just going to grind (sand) away the spots till inner area is exposed, if needed, insert more rust converter, body filler, primer and paint and eventually buff it out. Any first hand help would be appreciated. Please no off-hand responses or jokes...this is serious for me as we can't afford shop repairs or new car at this time. Thanks for any serious responses.