Licensing order

Dude!!!
You are getting a Private Pilot Certificate in either case!

However, I would suggest completing your certificate by getting the
power rating. I think you will have a much better understanding and
feel for airspace issues by completing the power rating. The glider
add-on will make you a much better stick and rudder pilot.

I think one of the problems we are having in the glider community with
regards to transponders and talking with airspace controllers and
towers is that many glider pilots never got comfortable with those
issues by flying power.

Besides, after listening to the constant drone of the engine and the
cryptic chatter on the radio while working on the power rating, the
peace and quiet of glider flying will be absolute heaven.

Guy