I have an SAR1. Bought it back in the 90's. It has some "slightly" canted sights and came with some wicked trigger slap. I tried all the fixes and finally put a Red Star Arms trigger in it. My wood is basically like yours, just a little more blonde.
I dont believe they came with a threaded muzzle, or at least mine didnt. Ive had AK's with brakes and AK's without. The AK74 type brakes do have a little less felt recoil, and enough so you can tell between a gun with it, and one without, but its really not that much of a difference. They are louder as they redirect the blast.
The slant brakes dont do anything other than look correct. If you want a muzzle device, a flash suppressor/hider would be your best bet, assuming your muzzle has been threaded. The threads should be 14mm left hand threads. If it was done here later, after the fact, you may want to verify that.
I was never a fan of the side mounts for the optics. Id used some fo the Russian "Kobra" sights and mounts and just never liked how they mounted or shouldered. The Ultimak handguard rails were just showing up and were an epiphany. With the right sight, you could actually cowitness your irons to the dot, and the sight was up front and out of the way. The rifle shouldered and shot just like it did with the irons, and you got the same basic cheek weld as you d with the irons. Once I figured out that the cheaper sights were a waste, and got my first Aimpoint, Id found my set up, and its been that way ever since.
I dont know where the 5000 round limit on the barrels came from. When I bought mine, 1000 rounds of 7.62x39 was still $75, and I know I have a good bit more than 5000 rounds through mine. They are tough, youll be fine.
This was my SAR back when I first got the Ultimak and was trying out some red dots. It had been painted, but Id stripped most of it off, and it was in between paint jobs.
This is what it looks like today......
Even with its canted sights, it still shoots well with ammo it likes. This was shot at 200 yards from a cross legged sitting position using the irons and Wolf 154 grain SP's, and fired at a steady cadence. The three round group towards the bottom was fired from a rest to confirm zero......
If youre a reasonable rifle shooter, they will do you well.