When in doubt, use shield oath. It's the same as having rampart on 24/7 for free and basically doubles the amount of enmity you generate. It will really soften up your gear deficit to just play it safe in tank stance.

As for gear, find whatever is cheapest but focus on left side. Right side only increases your HP. Left side increases HP, damage, and defense. If you can only keep 1 item up to date, make it your weapon. Weapon damage will have the most impact on your damage and enmity. (also you mentioned selling back gear when your done. As soon as you kill a monster wearing your gear it becomes 'unsellable' on the market board. You can only sell it to NPC shops for piddly amounts of gil.)