Hopefully, the seal problem with the bottles will work. I prefer the flippy top bottles like Grolsch makes. Usually gives a nice 'pop' upon opening.
I would recommend buying some light DME from a local brew shop and use that in stead of sugar. Mr. Beer is generally better with a good three pounds of extract. But using entirely Mr. Beer can get expensive real fast, that extract isn't cheap. I think you want a target ABV of better than 6% to have a good tasting beer. Stay away from the Booster as well, that is corn sugar and won't add much for flavor. Remember you're not just locked into Mr Beer ingredients. Moutons and several other alternatives exist. I recommend getting a 3 or 5 gallon carboy and airlock for a secondary fermenter. That way you can at least have two batches going at once. 2 or 2-1/2 gallons isn't much. By the time your beginning to like it, it's all gone. Maybe consider getting a second Mr Beer brewkeg (about $10) and then you can brew up standard 5 gallon batches, and save money.