Marshall is one of the coolest names you could give a horse but unfortunately it does not pass the profanity check.
My other cool horse names would be Deano, Dynamite, Maverick, Passenger, Deacon, Rodeo, Wrangler, Cheyenne, etc.
I personally go to gang camps like Shady Belle and Fort Mercer. Kill all the members inside and loot them. Usually get good stuff that you can sell at fences. Fishing is an effective way to get money as well.