1. If I understand correctly, with Mithral armor and Arcane Fluidity I would have a 5% arcane casting failure, is this worth while? Or is the difference between chain armor and a robe small enough it is not worth the chance of failure?
I don't have an elf or drow (and never will) so I refrain from answering this on the grounds that I will give wrong information.
2. With two levels of rogue, would I get any level 7 spells? I'm afraid I don't know the spell progression (levels 1,3,5,7,9,11,13 ?)
No, you would only get up to 6th level spells being you would be a 12th level wizard. You do have the spell progression right though.
3. For those times I am saving or out of SP, I have been using a shortbow (w/ pointblank shot) but I seem to miss 40% the time. I started with 16 Dex and would like to improve my change to hit. What am I missing or doing wrong?
Just face the music and realize that missing 40% of the time isn't all that bad. Wizards get a low Base Attack Bonus so you will often see a fair amount of missing unless you are attacking low AC monsters or have crazy high DEX. Some options might include looking into enhancements or feats to aid you with your archery, such as the Weapon Focus: Ranged feat.
4. (1Rog/2Wiz) When would be the best time to take the last level of Rogue? Is there a point I really need to boost (spot,UDM,jump,swim,tumble) in order to be able to handle rogue duties for groups? Otherwise could I take the last rogue level at 14 to get the most skill points possible?
The best time to take the second level of rogue is either when you cave in because you really want evasion or when you can spend all the skill points of the rogue level on those rogue skills without any waste. Without knowing the build you are using I can't give a precise level of when you would get the most out of your second rogue level, but the general principle is the rewards get better the longer you wait.
5. Any other advice that someone could pass along for a fairly new char?
Find people you enjoy playing with and find a character you enjoy playing. Toss out "best builds", "loot", "quest efficiency", and all those other metagame superiority issues and in the end, thats all that it boils down to.