You have a very simple (and great), static website that does not seem to open up a lot of programmable interfaces, other than the forum.
Assuming that you update all your software periodically, you should not be at much risk from anything other than the forum software.
As for being probed, all websites are being probed continuously by automated scripts.
It is my opinion that the biggest risk to your site is your forum software. Personally, I do not trust any PHP based forum software. If it was my website, I would personally host the forum with some security separation from the main website, such as on another server.
Everything else looks clean and simple.