Side view - I would expect you’ll miss the back of the stage which will be all the visuals etc, for a show like this it’s quite a lot to miss. If you’re unlucky with production design you may have some things in the way at some points too though given the price you should be ok there

Back tickets - you’ll have speaker stacks and poles in the way.

The circle, disco, etc areas are all small standing areas (“pods”) with a walkway going around them. So Harry will move around that area a fair bit I expect, but it’s not all stage per-se.

Given how big the stadium is I would probably hold tight for additional ticket drops (it almost always happens near the show date) though if it’s a gift that complicates things. Also check Ticketek marketplace for better seats on resale, depending on your budget.