Right back is definitely a problem. I would consider playing Tierney there even though on his wrong foot. McCrorie did play fair number of games for Bristol towards the end of the season so might be worth a go in the friendlies.
Not sure I would be taking Doak or any player who is not playing first team football. That said we are really thin upfront and no idea who we can take. Luke McCowan with 10 and Bruce Anderson with 7 are top Scottish scores in the league after Shankland. Ryan Hardie at Plymouth with 13 in Championship for Plymouth might be a possibility. Ross Stewart managed 4 games at the end of the season after coming back from injury which probably isn’t enough to get him into consideration.