Hehe, I don’t think PHP is popular around here, I am sure @codinghorror et al have some strong opinions about it 
Dicourse is written in a framework called Ruby on Rails, but that’s not really important.
SSH is nothing more than a protocol to connect to your server. It does not have anything to do with the installation per se. So you really don’t need to worry about this part, as long as you have a strong password.
Actually, installing discourse is safer than installing other software. It uses something called Docker, which is basically a box/container that is more or less completely isolated from the rest of your system. Which means that…
everything should be contained and you don’t have to worry that much.
That is not to say that it is very easy to install. I would suggest you should definitely try it. In order to be completely safe and worry-free, I’d just rent a separate VPS (folks here recommend Digital Ocean) and try the official installation guide.