wic;
Welcome to this forum, and congrats on your acquisition!
You don't mention year, but there is no such thing as a P1800S designation...earliest models were designated P1800, later when production was moved to Sweden, designation was changed to 1800S, last injected models were ...E and ...ES.
As the owner, the final decision on changes/mods is of course up to you, but if the vehicle is currently all original, and as such a good snapshot of the automotive state of the art, and particularly of the model at that time, you might consider keeping it original. Most here, including me, will probably prefer and advise to keep it historically original...that is, only consider changes that were originally available and period proper (ie Minilite wheels [like Simon Templer had fitted!], bullet style wing mirrors you were asking about)...to that, I would add safety and reliability changes which are only mildly invasive and which remain reversible (ie Pedal Position Sensing Brake Light Switch, and Pushbutton Start Switches - Full disclosure: I offer these kits.*). Finally, installing modern, radial ply tires is a no-brainer...
Enjoy vintage Volvo ownership! And when questions come up, know that there is literally a world of experience available here to help.
Cheers
* See:
https://www.sw-em.com/swemkits.htm