I have troublesome PIL (NC now)
My advice would be to treat your adult son, and his adult wife like adults at all time. You may have a difference of opinion to them at times but they are allowed to have their opinion too. They are allowed to do things in a different way to you and you should respect that and celebrate that you raised a son to this independent point.
If you do that you should be fine. 
Do not welcome her to the family by handing over the 'wimmin work' at the wedding reception, making your DIL responsible for all family birthday and Xmas cards and gifts which I never took onboard.
Do not insist on anything at the wedding. Not guests, not flowers, not anything.
Do not 'have words' with the bride at the reception (this was FIL, but MIL backed him) about how she'd better start behaving properly now, or she'll not be welcome in your family. It might limp on a bit, but eventually she might take you at your word...
But you sound great, and a bit like my Mum, who welcomes and accepts everyone. She worries about overstepping too but really doesn't. Just be happy for them, that's all they really need/want.