I don't think you'll be able to gain for long on SS with those numbers. That's good news and bad news. Good news: awesome, you're not terribly weak. Bad news: the days of easy gains are almost over. So milk it for what you can.
As for transfer from 3x5 to 1RM: you can do a set of 5 with a little more than what you can do for 3x5, and that set of 5 is going to be okay at predicting your 1RM. Or you can guess that you might be able to get 7 reps with your 3x5 weight and use that as a basis for guessing at a 1RM. A good rough guess that will be wrong but will get you in the ballpark might be that your 3x5 is around 85% of your 1RM. Again, this may be off considerably and depends on a lot of things. The only real way to figure out your 1RM is to test your 1RM, and even that isn't great info because, if you're a novice, your 1RM goes up after you recover from each workout. Don't live and die by your 1RM.
EDIT: but as for transfer, yeah, there's a lot of transfer. Before I was done with linear progression on SS, I went to a competition, squatted a tough 182.5, missed a 100kg bench. Before I was done with SS, I squatted 400# (which is like 181.8kg) for 3x5 and last night I benched 100kgx3x5. I think I've gotten stronger...