Highly recommend popping the Biomass power and going ham while it lasts. Then tip-toe very carefully. That way you'll be able to familiarize yourself with the situation you are in and learn the lay of the land. After a bit of learning process you can clear mines without Forsaken powers, especially with a bit of spellcasting.

1* and 2* seekers are just as hard as fulings of same level when you first arrive in plains.

High level seeker soldiers are probably somewhere around 2* berserker levels.

For those encounters you'll definitely want some superpowers, or at least magic. The first time I entered mines, there was one of those creatures, I no longer remember which. I died, and combed through 3 or 4 other mines before I went back to the first one to get my original stuff back. It's doable, and before long it won't be too challenging anymore.

Edit: 120 health is not enough. You'll need over 200 and health potions.