Removing the flow restrictor wont help, as the knuckles in the modern shower head set-ups are too small and wont allow sufficient volume of GF hot water through. Best detach the old rose head from the pipe/knuckle set-up, throw it away and then find a rose head that you can adapt to the old knuckle /pipe set-up. It's what I did when I reno'd my bathroom and every thing works fine - good flow with good temp. Plus, you can also buy pressure equalising washers for the cold tap which will give you even more control balancing the hot and cold water.

I just finished our new ensuite, which has a 1600mm vanity. I have 4 lighting circuits (switches): 1. 2 x downlights for the main bathroom in a similar place to you. 2. Another 2 x downlights ( 1 over each sink) 250mm off the wall (vanity is 500mm deep so halfway between person and mirror). 3. Extractor Fan / Heat Lamp and 4. Strip light under vanity for late night trips. The downlights are dimmable so you can have the main bathroom in a medium light and then you can choose how much to crank your vanity lights. The idea is that the light should shine onto your face hence they are installed in front of the person and they are on a gimble so they can be tilted to point at your face. I think you are in Australia so I can tell you they are the Domus Aqua Tilt 13 and are fully sealed (ip65) so no issue having over your shower, etc. They are also very bright as the light bounces off the white tiles, so really they are only needed when applying makeup. It's hard to know exactly where your lighting needs to go when you just have plans in front of you, but you could always get your electrician to wire both for wall sconces and downlights and then when you are further along you can choose whether to cut downlights or have wall lights. (Remember to take pictures and measurements of the wire locations before they close in the walls / ceiling!) If you try downlights first, it's also a lot easier to change your mind (i.e patch a ceiling) than wall lights as that usually means drilling through tiles..

You will need to re waterproof the whole lot if you try to take it off and replumb. There is nothing wrong with it functionally and the picture you have is just a picture of how it can look like not on how it should look. Placement is personal preference or at the installers discretion if you didn't specify. IMHO it looks good as they are both at the same height and it looks better , also not a fan of doing or having what is the "norm" or what everyone else has.

Swapping the shower with vanity would still look good. You could have an opaque shower screen. Also with the current layout the shower recess would be reflected in the vanity mirror anyway. This would also keep the wet area on one side, bath and shower, and the dry areas on the other, toilet and vanity. The only negative is that the toilet looks private with the current layout and shower wall. Moving the vanity may make the toilet less private.