Jumping ahead, that's good you're thinking of preserving the hardwood floor for the next Homeowner. However, they may or may not want to refinish it either, OR, maybe it can't be refinished. I see you got an estimate of $500 for refinishing so I'll go w/you on that it can be refinished.
Stepping backwards not ... I'm not a big fan of floating floors. They have a hollow sound when you walk on it. And since you're glueing it, unless the glue 'acts' as a rubberband does when it's streatched and 'bent', the glue will come loose over time. Sure, it's a personal preference as to how you end up doing your floor, so what you're planning on doing isn't wrong. (I just want ya to know that 'I hear ya'.) This plan would best preserve the floor below if that's what you want to do. BUT, if you want a 'nicer/better' floor, you have to niks the 'floor preservation' idea and go w/something that you can nail or staple. (Just my thoughts.)
As for the gaps and grooves, if you have a humidifier, turn it up to 35-40%, all year 'round. This will add humidity to the house and help the wood expand. BUT, before you do, clean out the gaps as best you can, preferably in winter when the house is driest. (Summer is worst because the wood will expand w/the natural humidity in the air ...)
Your proposed plan will do it all. But as you can see, I'm a bigger fan of redoing the real hardwood. Again, do realize the floating floor is hollow-sounding, and the glue will start to give out over time.