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Smith machine squats aren't whats hot in the streets for 5X5
Barbell squats are the core component of that program. You simply can't do the program if you can't squat freely. The smith machine is an entirely different exercise. Does all the stabilizing work for you, its no better than a leg press.
You would be better off using the dumbells and doing Bulgarian Split Squats instead of Smith Machine squats. It would be harder to 'progress' because the dumbells jump too high in weight too quickly for your legs to adapt, but you could just repeat the weight for a few sessions before you move up.
Or just get a membership to a real gym. You at Planet Fitness?
For the record, dumbell overhead press is a great substitution for the barbell overheard press. That is entirely acceptable, and for me personally is preferred because of the ability to stay away from your stronger shoulder doing most of the work.