Personally, I'd keep them separate. The bath would need a screen or curtain, which makes using it as a bath a little less relaxing. (I'm a massive bath person!)
I used to have a shower over the bath and HATED it. Then we moved and only had a terrible shower! 10ys later I finally got my bath! No compromises!
I did a walk in shower and got a big bath then had a sink unit made bespoke with a sink in the middle a worktop in marble around the sink so there's plenty of space for our things plus a tall cabinet either side. One for each of us.
I did push to maximise every cm of space, so much so we had to install a sliding door!! But its worth it. Looks amazing. And we got a cool barn door style sliding mechanism that looks a bit industrial so made a feature of it rather than it looking like we ran out of space for a normal door!!
If you plan to do your downstairs loo at some point, maybe the shower down there can be swapped for storage?
BUT it is your space, you will use it, so me hating a shower over the bath is just my own opinion, and if you are happy to have that in order to have extra storage then I'd say go for it and find a way to make it look nice. I'm sure there are also some lovely bath/shower designs that could tick the box.
I'd also be open to getting something bespoke made if you have space limitations or want to make use of every inch. It's a bit more money wise, but I'm so glad I did that. Looks so much more expensive and posh.
I actually downloaded a floorplan app, set up the room to the right measurements and played around with layouts. All possible options. With and without baths, showers, cupboards etc. You can then mull over them. Might be helpful to have a visual reference? I spent a few months deciding on layouts!
It was also helpful because I worked out what I could get away with (ie, we were able to get a bigger bath than we originally thought!)