Hi Cherries82,
New Ipod touch was released in September this year so i don't think there will be any new models in the immediate future.
All apps (charged or free) are forever. If changes are made to apps you will get updates for nothing. You control them exactly the same way as your music. You can choose which ones you sync to your Touch. They also take up very little room on the Touch. Check out the iTunes store for what Apps are available, some great little games plus lots of stuff for Health and wellbeing which could be good down the gym.
Interactive apps will obviously only work when you are in wifi range at home or where they have free wifi access.
Battery life for me seems pretty good although I mainly use it for music rather than video. Although it has been great on flights for watching films.
Best to keep screen brightness down and not use the internal speaker to prolong battery life.
The touch is controlled in exactly the same way as any other iPod. You can do it automatically or manually and just select the stuff you want.
All in all a great product for music, flims, podcasts, Apps, games and photos.