I have re-installed NextCloud Pi today and it has all gone very smoothly! (Almost too smoothly)
I ran the set up wizard and selected not to use USB storage (I might change this at a later date).
I selected not to use DDNS as I plan just to use my IP for the time being until I am more comfortable with everything and decide I want to use NextCloud on a regular/permanent basis.
I also selected for NCP to try to automatically forward ports
Is there a way I can verify if ports have been forwarded successfully?
For ports; from ncp-config or ncp-web:4443 run nc-info, it will tell you if ports 80/443 are open on Rpi. To check forward from outside, log in to your router interface or visit your external ip.
Is up to you, you can view or change passwords with nc-admin for NC user and nc-passwd for ncp-web user.
The wiki in general will give you good idea of the configuration possibilities of NCP. I usually run letsencrypt and set up automatic backups. It depends on what you are using NC for, personal preferences, etc.