You must notify the DVLA when you get a Dx of MS, Steph, and you should also notify your Insurance Company as well (that is in the small print as something like “… notify any material change which may affect your policy …”.
The second one is easy - I have never heard of anyone being refused insurance (but there could be someone out there who has), and they probably will not even acknowledge your letter.
The first one is tricky. If you have only had a verbal “probably MS”, and no written confirmation, then you could take a chance and wait until you see it in writing (but don’t leave it too long. When you notify the DVLA you will get a form to fill in that will ask what your condition is (yes, I know, you have already told them) and they will see that it is a neurological condition (if you have ticked the right box), and will then go to your neurologist (or whoever you have put down) and ask for a report, and then refer it to their medical panel and then make a decision. This can take some time (typically 10-14 weeks). What you do not do is to hand your licence back when they first ask for it (“oops, I forgot”)
The alternative is to hand in your licence on the grounds of a temporary condition, and apply to get it back when your eye improves. This might only take 1-2 weeks.
Only you can judge how fast your sight is recovering, and when you will be OK to drive. The DVLA are a bureaucracy, but no problem if it looks like you are playing by their rules.