There are a lot of different questions here, and unfortunately we'd probably need to discuss things to work out answers to some of them (not so easy here, as you can't reply to this unless you register, only post again).
The first question I'd ask is, how much free space do you actually have? That will tell you whether there really is a space problem (I assume from the way you've said it that the 5 apps aren't 5 recent 3D games - if they where that could really have eaten a lot of your space). That space is used not only for user-installed apps, but also app data (all apps), caches (temporary files). You can free some space by clearing caches (can be done app-by-app, or there are many cache clearing apps in the Play Store).
I can't comment on the camera because I don't know what's normal for this phone.
One question which occurs to me: when did these problems start? In particular, did things get worse after an update (it didn't originally come with 4.2.2)? If so it might be worth backing up any important data and doing a factory reset - sometimes it helps to make a clean start after a system update (though I can't promise this is anything to do with your problems).
