Hi, welcome to AO,

I would say that your 75 hits is not abnormal. I assume that you are referring to "connection attempts" rather than actual port scans. I have just looked at mine and I had 11 hits in the last 6 minutes, but only one was a port scan. The rest were typical internet "noise" If you are getting repeatedly hit from the same address then you may have some cause for concern.

The internet is still inhabited by a lot of unpatched and infected machines that have network aware trojans that are scanning the ISP subnet. I suspect that if you look at the details you will see a lot of them are harmless "pings" and that most of the other stuff has originated from within your own ISP subnet. At least that is how things are here.

I am no expert on routers, but they are physical devices and potentially more flexible than a standard home software firewall. I would certainly want one if I had a fixed IP address.

Hope that helps a bit