Record Types are really only necessary if you need different picklist values for each "Type", or need a different page layout. Otherwise they are just a glorified picklist.
So:
I would create a picklist with Sales/Service and make it mandatory on the page layout
I would create another record type for simplicity (just start from scratch), and dataload all users onto the new Record Type, at the same time populating that picklist value
Change all profiles to default to this new record type, and then delete the old ones
I don't think there is much you can do with Contact Roles - you are pretty limited there. I wouldn't get your hopes up on that one, you might need a custom object instead.
Reports: Filtering/Grouping by a picklist vs a record type is the exact same thing. You'll have to adjust existing reports of course, and add your new Picklist Field to any custom report types you have created
The picklist field should solve the Marketing Automation request as well, otherwise just have a workflow populate a checkbox when the picklist is marked "Sales"
you could delete the one that you don't want anymore. By doing so, it will ask you it you want to replace the Deleted Value with an Existing One. So you'll be able to select the existing Record Type.
So:
you could delete the one that you don't want anymore. By doing so, it will ask you it you want to replace the Deleted Value with an Existing One. So you'll be able to select the existing Record Type.