Better late then never!
A lot of it depends on what kind of riding you are talking about. Will it be mostly city or highway? Is the commute long (one-way), will you be taking longer trips?
You're current insurance company will insure you with your M1 only and as stated in
this thread there are plenty of options for once you complete your M2 Safety course as-well.
You can save on cost for insurance as-long as you're getting something lower then 600CC and its not a super-sport.
The newer the bike, the higher your premium will be, even if its exactly the same thing, just produced one year later as was the case with my R3 (2018 VS 2017, both brand new).
Your best bet is to call around, speak to various agents from different companies and definitely try brokers whom will probably have better deals.
You will need to get actual VIN numbers for the bikes you want to check your insurance with so that you're able to get legitimate quotes vs theoretical ones.
I found that most companies did not care for how many KM you were riding throughout the year so there's that as-well.
If you are planning on getting something fancy, make sure to protect yourself in the case of theft which unfortunately has a high chance of occurrence.
If you're not after fast acceleration or crazy top speed, you can look at 300-400cc bikes and still enjoy the ride however keep in mind that you'll probably grow bored of it after a few months so you may as-well look at 500's to get the best bang for your buck (so to speak).
EDIT: Keep in mind that there are other things that are also very important like seating position and this varies from bike to bike so go to various different dealerships and sit on all the bikes you can. Take your time and try to get a feel for what it'd be like sitting on the bike for long periods. Super-sports for example really lack in this dept. and that's why a lot of experienced bikers over the years go with sport tourings or cruisers despite starting out with sport bikes.