I have a client that has several years to file.

2015- corp tax 1120

2016-2020 1040 

2015-2018 he owes money and 2019-2020 he gets a refund.

should i file all the taxes at once and wait for the letters to come and then do an installment agreement ? or should i file an installment agreement for all money due with the 2018 taxes? 

i feel like i should file them all and wait for the irs to send letters with the amount due then file for an installment agreement.

what is your advice?

also what is the form to file an installment agreement for a corporation?

thanks in advance.