I can do this by leveraging more than 20 years of Linux SysAdmin experience. I normally work directly in bash instead of using a control panel (Plesk), but I can work with it if required.
I cannot gurantee you 100% uptime on your website. There will be reasonable situations (kernel upgrades) that require a reboot during which your website will be down. I might also need to restart the webserver after an upgrade of one of the packages in the chain which will cause a minimum of 30 seconds of downtime. This is perhaps picking nits, but I want you to understand the limits of what I can promise you.
Backups are not difficult to deal with. Again, normally I would write a python script to do this, but I will look at the available options in Plesk and use that.
Security. This can be a big job depending on the types of software you run on the website and on the server directly. If, for example, you are installing WordPress modules, I will need to audit those. Security auditing is not outside my normal skill set. In addition to being a sysadmin for many years, I have been writing software for about 25 years and using php for the last 10 years or so.
I look forward to hearing from you soon.