don't do it. do starting strength instead.
Yep. You're actually the ideal case for SS - chronically underweight, weak and needing to gain strength and mass. Doing a full smolov with a 250 max or whatever is just silly imho. You can probably easily set a PR every workout squatting 2-3 a week, why bother with smolov?
I'm currently doing smolov jnr which is gentler than full smolov cos its wavy in intensity meaning I get to practice a lot of squatting with submax loads because I have form problems and need a lot of practice. So far so good, ive improved a fair bit since last month. I also didnt start with a true max (i did 137.5kgx5 with shitty form done belted earlier this year at 87kg BW) and instead picked a fairly conservative 122.5kg max. I'd actually be fine with my max staying where it was as long as my form improves.
Having said that - devils advocate - why not do smolov early? If you are working hard on form, it will cement the movement pattern which is a good thing. It will give you plenty of practice to learn the groove of the lift. The weights aren't heavy enough to hurt you (maybe maybe not, it depends on your form and the robustness of your knees etc) so it's less risky than doing it with heavier weights later.
But on the balance I think it's overkill with a 250# max. If you're that keen on smolov why not jnr?