I made a SEP IRA contribution on my 2018 tax return. Can I also make a Roth IRA contribution for 2018? Can I make the maximum contribution which for me is $6500? Thanks.

It depends.

Your contributions to a Roth IRA may be reduced or phased out depending on your MAGI (Modified Adjusted Gross Income).

Please see this IRS document to determine if you are eligible to contribute to a Roth IRA:

https://www.irs.gov/retirement-plans/plan-participant-employee/amount-of-roth-ira-contributions-that-you-can-make-for-2018

Our combined income was well below the phase out amount base don the link sent. Thanks.