As seen here on my system same thing 97% cpu but only one on of my cores So it's 97% out of 400% of my cpu is being used (I have 4 cores)
How many connections do you serve with your configuration?
I have now set maxconnections to 10, and my one core load has dropped to around 50%. The totalbytessent rises fast, so I believe the the cpu load is needed to serve the connections. In this case it's nearly impossible to serve 500 connections simultaniosly.
I have a limit of 5 TByte monthly internet traffic, and try to increase it. Doge alone will fill my traffic limit quickly.
Either way unless you are using 600% of your total cpu resources, You shouldn't worry, using max % of just one core is nothing. You're way below the threshold. And changing the number of clients you're connected with does indeed indicate there's more cpu load congruent with network usage. So that's normal.
You do however have a bigger concern with the data cap on your service plan. That needs to be addressed sooner than later. So either connect with less nodes, or change your traffic limit. Firstly keep an eye on how much data transfer occurs over say a few days, then you can determine how much you'll need and make adjustments from there. Keep in mind every new node that might connect with you to do a full sync will probably average you at least 44 gigabytes or more a day (depending what your upload speed is). Which is also something else you should be able to limit, Rather than the number of connections but actually slow down your upload rates