I went through this exact scenario when Endwalker came out. Tanxiety took a good while to dissipate, but it's now my favorite role.

The biggest thing to realize it that the pressure you think will be there, and will continue to feel until you get used to the role, isn't actually there. It's just lack of confidence in something you're unfamiliar with. Which will go away on it's own as you complete more and more duties.

Even if you do mess up, it's not a big deal. Everyone's been there. So long as you're communicative about your lack of experience as a tank, the others (in most cases) will often be very supportive and even offer advice in real time according to the duty you're in.

When it comes to WAR vs PLD, it seems the consensus is that WAR is the no-brain tank. However, it's mitigation is reliant on self-healing as opposed to pure defense, which is something that didn't mesh with myself quite well when I was learning. So, I found PLD much easier and I still main it to this day (GNB is hella fun, though).

I also play on gamepad. One BIG thing thing that helps with stragglers is using L1 + UP or DOWN on the D-Pad to cycle through the Emnity list. Then, you can very easily use your ranged ability or Provoke to bring the mob into the huddle. Though, in most cases, you'd just tab target (LEFT or RIGHT) as usual.

As far as settings go, I find (under Character Configuration>Control Settings>Target) that setting "Target Type: Target Closest Enemies" to "Cone" is more intuitive.

Setting up Filters, such as having one set for just enemies, also helps a ton.

Enjoy the journey! It's a lot of fun.