don't go gauss too willingly as forge, it cost a bit more than you want and you don't need many hogs once tech 3 is there.
800 for gauss is a bit much, tanks or hornets tech 3 and move away from the gauss. you can still put in grenadier hogs, they do well enough and are great building damage.
against prophet, its good to get tanks out and rolling while keeping control of your half of the map, if you can push him back, you will probably win so just be on defencive but still keep at least a good chunk of map control. just make sure he doesn't go flying, it gets really annoying as unsc if he pulls that off but you should be able to keep his units down and stop him from teching that much.
And burn, you will burn. You will burn in hell, yeah you will burn in hell. You will burn in hell, yeah you will burn in hell for your sins.