I recently finished a hard maple dining top with Oxford 9000 Super clear Polyurethane Satin finish

I had the worst time brushing on without brush strokes and bubbles, especially at the edges.  I have read up on this and followed guidelines to the Tee, but could not avoid very noticible lines and bubbles.

What can I do to buff these out.  It seems like the film is very thin and I think I am buffing right through it with 220 grit. 

Does pumice or rottenstone work with waterbased?

Can I add more coats, even after a few months of use? and then buff down?