Shooting a red dot at 300 is not hard and 7.62x39 is more than capable of doing well, but experience matters too. If you don't shoot well at 100 you will do poorly at 300, but if your fundamentals are right 300 is no problem for 7.62x39 and a red dot. Keep that in mind if you try 300 and don't have any luck...it could be you
For red dots get a Primary Arms or the Holosun ACSS. They both have really good track records and large fan bases with very few complaints.
Ultimak is fine. If you install it properly and don't remove it zero is good and it has a long and proven track record.
You may like the Tula ammo but you should try a few other brands of x39 in a controlled bench situation to compare. It doesn't mean you have to buy thousands of different rounds if Tula sucks in your rifle but if you test it properly you will know it's the ammo and not the rifle. Test it with an optic if you can
As engineer posted, DON'T trade the WASR for the PSAK. Terrible idea until you prove for sure that the WASR can't shoot.
For side rail optic options,
check out my site. Careful though, combloc optics can be addictive
Z