Exercise Selection and Variations?

Im following pavel’s 5x5x5 method and have some questions about exercise selection.

The exercises ive been doing are, Front squat, Pullup, seated row, 1-DB push press, and leg curls.

I just switched to front squats, from back squats, and like them quite a bit. Should I abandon back squats completely, or do they still belong in a training plan?

Also, I read somewhere on here about HFT and the author stated that the key was slight variations in exercises, like hand placement or feet width, etc. But Pavel’s plan is based on learning through doing the same movements with a high frequency, and knowing what weight to use as well. If I start changing my grip and feet placement, then I dont think i’ll know what weight to use

Lastly, I dont do much overhead pressing, or olympic overhead lifts, and feel im missing out. I would probably like to eventually be doing overhead squats, but how do they fit into a strength plan?