It's good to hear that you're happy with the results of your upper. I'm not the best person to be asking about full lower dentures because mine are partials. I still have two lower canines which don't hold the denture down but they do a pretty good job of stopping them from shifting from side to side. I didn't have the same problems full lower denture wearers have so I can't tell you first hand about the problems they faced.
I expect that a full lower denture won't fit well until until after a hard reline or when you get "perms" because until then the gums are going to be constantly shrinking. The first month will be the most difficult because the gums do most of the shrinking during that time. The denture will eventually fit though. If you managed well with the upper (and it sound like you have) you'll probably do ok with the lower. Adhesives, cushions and other products can help to keep the dentures in place for both talking and eating so I don't think you'll have to worry about the teeth moving.
I hope I've helped to answer your questions. I would suggest you post your questions to the board. With a little luck you'll get some feed back from people who were recently fitted with full lower dentures. Good luck!