I started zafaria at level sixty, and got out at level seventy one, you will probably get out at level 72,73, or 74, don't worry if you are to late to Avalon, even if you get there at level 76, you would be fine. so don't worry about being late.
I started Zafaria around Level Sixty and didn't finish until Level Seventy-Two. If you start or finish a bit earlier or later, that's absolutely fine! It all depends on how many side quests you have done from other worlds. I haven't done very many.
Honestly, it will depend on how many side quests you do. You can Bash through the worlds by only doing main quests, and get 8 - 10 levels, or you can do all the sides and posibly make 12 - 15.
How you play is completely your call, and will have severe effects on the "Exact" number of levels you gain...
I'm a balance wizard and I do ALL side quest. I started at level 65 and finished at 74. (I didn't do much side questing in zafaria but I'm gonna go back to do them!