1. The bubbles probably mean there is a respiratory infection. See a vet. In the mean time, be sure your tortoise is warm enough. Don't overheat him, just be sure he's not getting chilled.
2. The white poo is probably normal. It's like what birds do. Do mention it to the vet, though, because there are times when it can indicate a problem.
Keep it slow and steady.
PS. Please post back to let us know how you get on.