Do you have access to some kind of bike co-op? You can often find lots of vintage parts at co-ops. they often have used wheels, it’s how I find 700c wheels for 700c conversions.
Tires? I use Paselas, just like the 27” tires. If your 27” wheel set is in good shape, it will be way cheaper to just get a new pair of tires. If you want a project or can easily/reasonably find 700c wheels, go for it.
My ‘81 412 took 700c wheels easily. It also helped that I swapped out the Dia Compe side pulls with 610 centerpulls. I can just barely squeeze 35’s and fenders - it’s quite tight. 38’s without fenders is also doable.
For way less than $200 you can find a nice SR Apex or Super Custom crank in 86 BCD and have options all the way from 28t on up and you don’t have to worry about two different BCD’s. It’s what I put on my wife’s 710 and my 412. She has a 45/28 and I have a 50/45/32.
This one is not my favorite with the imperfect taper, but has the perfect rings for your project, just remove the 50t, swap in chainring bolts for a double and Bob’s your uncle! Might not even have to change the spindle in your bottom bracket!
We both have long cage rear derailleurs to handle the chain wrap. Your Suntour BL 3600 (S) should be able to handle it.