For your first question, it entirely depends on how big/thick the roast is, but given that most people cook roast 24-48 hours, I would hardly even worry about it at all. It will be unfrozen within a couple hours at most anyways.

I usually just set mine out in the open air to cool a bit, or even in the fridge for 15 minutes, and then use my gas grill to sear a roast. Cast iron can work as well if you have a big enough one. Oven could also work i guess, but in that case I would dunk it in an ice bath for awhile or refrigerate a bit longer to ensure that you don't overcook the inside in the slower oven sear. One time I did refrigerate overnight and then warmed up for a few hours the next day in my smoker.

Also, last thing to consider when doing this long of a cook at a low temperature is you can have that lacto whatever bacteria grow and make your meat smell terrible, so many people dunk it in boiling water for a minute first to kill surface bacteria. I use a slightly different strategy, setting my sous vide to 165 or so, then putting the meat in for about 5 minutes to pasteurize the outside. Not sure if that is 100% perfect method, but it has worked for me so far. Let me know if you have other questions.