TORX size

Welcome back to 2CarPros. The hand tools are the issue. An impact with an impact rated bit would break it loose. The reason for that is that the instant high torque "hits" of the impact will break the bond of the factory locking compound and the locking design of the threads along with the torque they are installed with. You don't need to get a cordless or air impact (although they would be better) Instead get an impact that you hit with a heavy hammer. They are available in many auto parts stores and even Lowes, Home Depot, Harbor Freight.
As for the bits, the day I find ones that don't break I'll let you know, I've broken just about every brand out there. Snap-On, MAC, Matco, S&K, Proto, Lisle and most of the house brands from the parts stores. I usually buy a set, then as they break I buy a couple spares.
I think the current ones are Lisle or Sunex. Because they all tend to break I don't buy the top dollar ones, I figure the extra money can buy two to three spares.
However there is a special bit for them you can get at many places like NAPA or online. It's an OTC 5901 set, made for seat belt bolts. Most times you can use a hammer and use a T-50 bit as well.

Nope, I've had days when the truck would pull up and I'd walk out there with a coffee can full of warranty tools. These days I try to let air or battery power take the grunt work. The battery impacts are great for most things. They hit a bit softer than air but they hit a lot faster than most air tools. I find I break fewer fasteners and tools with them.