Quick fix… buy some more horsepower. A better, faster server or server account.
Possibly a better fix… update your PHP. You are running 7.0.33. I recommend 7.3.X which would be the latest, greatest.
Move everything other than the web services off of your server… let your domain provider or CloudFlare do your DNS. Move the email elsewhere. Cron tasks, too.
Pare down your running plugins…
Move half your hosting load to another server. Host the site elsewhere but leave the database where it is or vice versa.
Consider Cloud-based hosting.
Maybe a CDN.
Add a cache… better yet… add a proxy box out front. Your host ‘One and One’ might already offer that.
CloudFlare might help once you get the site speed up better. If you don’t fix the response first you’ll get 500 errors from the CloudFlare free tier.
Build a local box to offload the creative side of things like new posts, pages, and such and synchronize those manually or with a plugin.
If you are running the Broken Link Checker plugin then go in and change the default settings from 72 hours to something like 480 hrs and lose the extra features. Tell the BLC to only run once an hour.
Back to CloudFlare… CloudFlare’s DNS might help block anyone trying to abuse your site via DDOS attacks.
A firewall like WordFence might help.
Look into IP blocking foreign servers from troublesome areas and anything outside your market area.