I have both a 50 PLD and 50 Whm. First, queuing up with random people in DF is going to be very difficult to begin with as a fresh tank jumping in with people wanting speed runs.

STAND YOUR GROUND. Know your limitations. If the group aren't asshats they'll be respectful. Just know, you're going to lose agro. There just is not a chance you're going to hold agro against 2 geared dps.

With finances in mind, buy as much top end gear as you can, as mentioned lvl 49 accessories, crafted armors, etc. I would recommend NOT trying AK. Queue for WP over and over and over and over again. 100Tomes per run just start equipping. I dont think one upgrade will be better than another, just start equipping from worst item up. Weapon plays a massive role so get Ifrit and Garuda down asap. As a PLD you'll be lucky in ifrit because you're a stunbot and should be easy to get your weapon. WP, WP, WP, WP, WP, WP, WP....um...WP?

Edit:
Dont worry about your epic until it's time. By the time you're done with Titan you'll have more than enough tomes anyway and even if you dont. once you're geared and can do 20minute or less WP speed runs you can get 900 Philo's easily in an evening. Also, IMO, don't buy ANYTHING myth related. Get +1 first...myth tomes will take you 3 weeks to save for +1, start now.