Can I file WI state return now without requesting homestead credit even though I am eligible? I won't have my rent certificates until after tax deadline.

You can file your Wisconsin return without filing for the homestead credit. To file your homestead credit at a later date, please see the following from the Wisconsin Department of Revenue site:

If you previously filed your Wisconsin income tax return and now wish to file a claim for homestead credit, you should write "Income Tax Return Separately Filed" on the top of your Schedule H or H-EZ. Before mailing your Schedule H or H-EZ, attach the following behind your claim:

• Your completed 2016 rent certificate(s) and/or a copy of your 2016 property tax bill(s),
• Other homestead credit notes, schedules, or legal documents,
• A complete copy of your income tax return, Form 1, 1A, WI-Z, or 1NPR (write "Duplicate" at the top of the Wisconsin tax return copy),
• A complete copy of your federal income tax return and all supporting schedules if the previously filed income tax return was a Form 1 or 1NPR,
• Copies of any wage statements, Forms W-2, W-2G, 1099-R, and 1098-T.

Delays to your refund will happen if all the proper documents are not attached to your homestead credit claim.

You can see the following link for more information:  Homestead Credit information