43x is my everyday carry and does everything I need it to. That said, go handle several guns in the size you think you want, based on your needs. See what fits best, then research reliability, etc.
Smith M&P is also a strong contender. 9mm is the obvious choice for many, many reasons. Bullets...
Both of those powders work great in 6gt. I’d have to guess dasher and BR would be similar.
Creed likes h1000 and comparable
Edit to add that 109 is the heaviest I’ve run in front of those powders. Going to tinker with 116 and 120 this winter. Might need slower powder.
For someone that hand-loads and in a bolt gun, BR, Dasher, or GT are better options in my opinion. I have the latter two and they have been very easy to tune and produce very minimal recoil. Also had a HOWA mini in 6arc. Didn’t care for the mini platform at all.
I’m a fan of the attack pants. And the Sierra, guide, etc. I have several pairs nearing 10 years old that are still in good enough shape to wear regularly.
Missed this detail. As others have indicated, this is a dual injected engine designed specifically to minimize carbon build-up on the valves. The service they're recommending is unnecessary on these engines. Certainly doesn't hurt to use a fuel "cleaning" additive once every 15k-30k miles, but...
Should be done on direct injected engines. Not sure if yours is. Depends on the year. I’d ask details about how they do it. Hopefully not just a fuel additive. It should be run through the throttle body to take carbon off the valves.
I took a lesson at a local fly shop many years ago. Little tricks from an experienced instructor cut the learning curve dramatically. I passed those tips on to my boys and they both cast better than I do at 6yo and 10yo.