You can use 1-3 Abilities, so you have Powerstrike, I would have gone with Retribution as well, making 2. I do not like using Alt as a Hot key because it can cause issues. Other than hot keys, you can just click the emblem to highlight it and use it. You will find a method that you will like to use. (some people change hot keys)
Make more mules (you can create a total of 16 characters) to store stuff on. As for a Vault, you don't need one, but if you don't mind using FG to hire one for X amount of days, then do as you will.
If buying gear, make sure you buy your MQ gear first and build around those items (since you have some FG). Buy cheapest but effective gear @ level 1 (0 gear which is TierIII), Tier IV... if your level 5 gear is good, then buy items in 10 level brackets... so 0 (TierIII), lvl5 (IV), 15 (VI), 25 (VIII), 35 (X), 45 (XII) and MQ 55 (XIV).
Goodluck.