Yes. There are two levels of it as well. I believe it's under the upgrade tree for Kvasir's projects.

I did that later on, so I was pretty decked out. Slam to clear out bunched up groups of enemies. Shatter and Slam for the shielded guys. Vortex to prevent enemies I couldn't quite get to yet from attacking me. Vortex also makes the huge shielded guys more vulnerable. I can't remember if I favored the Assault Rifle or Charged Pulse Cannon there, but I'd use one of those while I waited for my abilities to cooldown. I'm pretty sure I got it on my first try.

Don't forget that you can craft health infusions (which can have their own perks, like fast recharging and some kind of quasi-invulnerability when you first use it), or you could use Overdrive and avoid enemies (giving your health a chance to fully recharge), so you don't have to rely on the Defib except as a last resort.

What augmentations have you been getting from the Cyber Doc at Wellspring? I prioritized damage upgrades, but maybe you should do health, if you haven't been doing that already.

First priority should be completing all the arks. Afterwards, or somewhere along that journey, complete the first story mission for each of the three Project Dagger partners. (Just to open up their Project upgrade trees.) If you do any camps/outposts along the way, try to completely finish them. You’ll want that feltrite.

As awful as the menus are, explore them thoroughly. Don’t hoard stuff for the upgrade trees. Always keep upgrading, and always have a plan for what you want to upgrade next.

From there, I set about clearing out the map, region by region. I referenced maps online to show me any locations I hadn’t already found. Once I’d done everything I could, I finished the four remaining story missions.

By the end, you’ll be so absurdly overpowered that basically everything is a cakewalk (on normal difficulty, anyway).

I don’t think any of the arks are gated by the campaign, but I can’t swear to that. They don’t all show up on the map by default, though.

https://game-maps.com/RAGE2/Rage-2-Game-Guide.asp

Yup. You can’t find BFG ammo in the wild. Every shot is $1,000, and it’s sold exclusively at Boom! in Wellspring.

I didn’t do any races beyond the single required one. I’d kill mutants I stumbled upon in the wild, but I didn’t seek them out. You’ll fight plenty throughout the campaign.

The upgrades boost your max health, damage inflicted, and overdrive capacity. There’s nothing you have to do once you get an upgrade — the values automatically increase.

You only have to win one race.

I didn’t get it on my first try (my third, I think?), but it’s not too bad. The race is relatively short, so it’s not too much of a headache to repeat.