Every-time you complete your maximum floor , it is recommended to reset. "Do I do the lowest floor for each class OSRS Gold?" I don't know what you intend to say by this question. The tendency is to rush for more xp however doing it all in one go can be more relaxing. This is a choice for each player. There are xp bonus points for the number of monsters you kill and for the rooms you go into. The reward for entering rooms is much higher than to kill monsters. So, always make sure you enter every room and only kill monsters if you would like or need to.
That's personal question. What do you like doing more? Training in a single spot or dunging to learn a variety of things? Fractite is a dung equivalent of rune. You could use it at level 40. Depends on training methods. If you are using guides, you'll probably finish most of them within one day. I'd bet at about 10 hours play time for each one, except for the three you listed.
You will need to decide what you're planning to do. A stronger strength is usually used for people who pk/duel. If range and mage are similar, and won't influence your combat skills in the event that one takes over your combat in melee. Normal oak - willows are usually the preferred choice to train in woodcutting. I could sell oaks, but willows I would be burning for burning.
Do you want the prayer option or straight atk/str/def levels? It's up to you to decide. Personally, I would like to have more prayer so I would consider hill giants. After the 40s I would say hill giants for additional prayers and flesh crawlers as previously mentioned. It won't be much of a change until the 1950s, in which time moss giants might be an alternate to the hill giants Buy RuneScape 2007 Gold. After you've reached the sixties it's time to think about the stronghold of security spiders.