Sounds like a plan AND I would recommend just doing the Roselaireblend. It's not that sour. You will be disappointed and it will be a waste (IMO) if you pitch a clean yeast first.
I do a lot of sours and fruit with the the sugars fermented out are often sour enough w/o a special yeast. However they are one dimensional.
Go with Tart cherries if you can. Sweet end up too cinnamony and lack that crisp bite.