If I had to guess, 15-17%.
I would not focus so much on an exact BF%, projected weight OR projected date to end your cut. I would just keep cutting until you reach a certain look in the mirror, whatever weight, BF% or date that happens to be. It took me many, many attempts to get really lean. I would say, I am going to cut to (blank) weight or for (blank) amount of time. I would start to feel skinny and small so I would stop, never really obtaining the level of leanness I wanted. It wasn't until, I started cutting and just kept cutting and cutting until finally my abs appeared, then I kept going. Actually, it took me 9 months to go from 25% down to about 10%. I did 3-4 separate 8 week cuts with reverse diet/diet breaks in between for mental sanity. At that time, I reverse dieted VERY VERY slowly by adding 100 calories per week initially, then went to 50 calories per week. I spent 6 weeks reverse dieting out of the cut, then hung out at maintenance for 1-2 months before ever bulking. Now I stay between somewhere between 8-15%, never losing full site of my ab's.
Back to your other question.................Personally, I would add 250cal per day across the board. Adding 250 per day, whether it be on a workout day or non-workout day, is still adding 250 per day. Not sure where you are getting 500 calories from.
I am not a fan of calorie cycling when cutting or reverse dieting. IMO it takes a simple process and over complicates it.
Let me ask you this to simplify:
What are your current calories on workout days?
What are your current calories on non-workout days?