WI is very anti spousal support so unless she has been a SAHM for many years or is disabled it will be unlikely you will have to pay much if any and it's doubtful it would be more than 2 years. I have never heard of anyone getting half of their X's salary for SS in WI.
As for custody WI doesn't neccesarily do a straight 25 percent. CS is based off of the number of overnights you have each month. You do NOT have to settle for EOW. Why not try for 50/50 placement? WI is very pro 50/50 and in most cases if one parent asks for it the other has to prove why they should not have it. In that case your CS would go down significantly and it would lessen the chances of SS. (which is slim anyway)
I don't check this board often. If you have any questions feel free to PM me.
When we were together, you said you'd die for me. Now, I think it's time you kept your promise.