My question is, what do I do with this $3200 basis. I didn't create a separate IRA for this so It's in the same IRA pot that I put in every year. Can I convert the 1600 to a Roth?
Backdoor Roth - Bogleheads will cover many (all?) of your questions. After you read that, what questions remain/popped up?
Note Line 6 of Form 8606: it wouldn't have mattered if you each had created separate IRAs, because the IRS treats all of a person's non-Roth IRAs as "one large traditional" IRA when it comes to determining how much of an IRA withdrawal/conversion is taxable vs. non-taxable.
I am not sure i understand the pro-rata rules. let's say my ira is 50k but that new non deductible basis is 1600. will i be creating a taxable event if I convert the 1600 to a Roth, bringing my basis back to zero?
Pro-rata means you don't get to pick and choose the pot; it's proportionately applied. So, $1,600 converted to Roth is ((1600 / 50000) * 1600) = $51.20 post-tax, and $1,548.80 taxable. This leaves you with $1,548.80 in non-deductible contributions left.
Yes, yuck. And, just like the guy who always steps 1/2 of the distance never gets to the other side, that stub will always be there, unfortunately. Be sure to keep track of it, so you at least get credit when it's due.
There is a small window of opportunity for 401k's in the same situation. If you roll over a whole deductible 401k with nondeductible contributions to an IRA, you get the opportunity to split those contributions to a Roth IRA, thus avoiding the mess.