Few Questions from an aspiring Monk

So should i build an Evasion or a -PDT set for these TP Heavy mobs, or both?

Both :3

Maybe a hybrid too, with both as much eva and pdt as you can put on at the same time.

Well, to be fair, most things that are viable for you to duo with a whm won't have extreme accuracy, so you might not need a whole lot of eva to reach the cap of 80% anyway. For a lot of content, it might be best to just focus on pdt.

With a pocket WHM you don't even need to bother with the Evasion and -pdt sets save for when you get to 99 and have made considerable progress through Abyssea. Even then, if your WHM has half a functioning brain you've got nothing to worry about, and if you're ever in a situation where something is hitting you that hard you've likely got fanny/fool's tonics at the ready. For everything else, there's cureskin. :3

Seal NMs go squish. Have fun with that.

Yeah, most stuff is unproblematic. However, for some NMs, you really want a MDT/MDB set. Even if you've got 4000 hp, some mobs like Rani can fuck you up. I've seen it nuke for 3000 damage to a monk with 5/5 shellra5 on him, for so to follow up with a magical TP move right afterwards.

Additionally, PDT can mitigate some damage for certain reduce-to-critical HP attacks, like ironclad's ballistic kick. It is very relaxing to see your tank be left with 900 hp after a ballistic kick instead of 150.

With brawny and Black Belt, you'd already be pretty much full-timing -10%PDT which is quite nice anyway.

Other particular items of note are: Augmented Dark rings from abyssea konschat gold chests (max 6% each) or Defending Ring (10%). Twilight Torque (5%) or Wiglen Gorget (6% -PDT +6% MDT). Either Fugacity Beret (1% PDT 12 eva) or an augmented Genbu's Kabuto (3% PDT 8 eva) or Arhat's Jinpachi +1 (6% PDT). Augmented Kirin's Osisde (5% PDT 7 eva) or Arhat's Gi +1 (9% PDT). Melaco Mittens (3% PDT). Molluska Mantle (5%). Darksteel Subligar +1 (3%). Plumb Boots (5%) or Darksteel Leggings +1 (2%). Colossus's Earring (1%).

Also Sheltered Ring is worth noting, as it will make 5/5 Shellra 5 give 29% -MDT, meaning you only need 21% to cap it. It also gives 1% regen while equipped if you're going for an idle set too. If you are, both Genbu's Kabuto and Kirin's Osode can be aug'd with regen as well. Note that these aug's can take a while and cost quite a bit to get.

If you can't get hold of any of the -PDT items, replacing them with Kacura/+1 for eva is a good second best.