Wow! Sounds like you're doing great - and your puppy has learned TONS.
"Leave it" is a really handy command, but so is "Drop it" - a release command. It can be taught in a really fun way playing fetch.
A 30 minute stay is ridiculous - and frankly, I would never aspire to work my way up to it. Competitive obedience at the highest level does a 2 minute down-stay. At this age, a 30 second down-stay is quite an accomplishment.
Instead of having an...