If it were me... you say you have some bare dirt.... I think you'd be ok. I'd seed it down really thick. Like, PERSONALLY, I go a little over-board on smaller projects like that cause i might get a little crazy with seed and herbicide BUT it's only a smaller amount of acres and if you spend a little more, who cares, right?!?!
SO... If it were ME, i'd go like 10 lbs to the acre of Switchgrass and I'd seed that anytime, BEFORE mid-march. Ideally in February. Or I'd see if you could light it on fire at all (pry not but might be worth a try?) to burn anything off BUT not critical to success- try and burn and then seed if you thought about that. that would remove some trash on top. Whether you do that or not.... Early April I'd BLAST the stuff... I'd be hitting it with 2-3 quarts of Round-up and 4-ish quarts per acre of Atrazine (ok, if you live in Iowa or many other places, only 2.2 quarts of Atrazine since that's the law) and walk away. If you're somewhere that allows 4+ quarts to acre of atrazine, I think you'll be able to walk away (unless the trash on top was super bad). If you get foxtail- you can get some herbicides to kill foxtail in switchgrass and I'd watch foxtail growth VERY CAREFULLY and react very quickly if it does come in. Read earlier on foxtail herbicides. I think it's do-able. Sounds like you have some round-up kill and some bare soil so I think you can get it done. Just do it right and do it timely and don't cut corners. Good luck!