Hey Jan,
nice to read your fast answer!
I just can tell you from my point of view and my experiences with all this stuff in the last 10-15 years. Hopefully I don't forget something.
You have to ask yourself what's the benefit for you and the visitors of your site, will something be better with a CMS and do you really need such a bloated system for your project? Is it worth it to always have a look on it if it's not beeing hacked? Keep in mind that HTML 4.01 (Strict) is supported very well by all platforms and devices.
I just had a look on your page with my mobile phone and have to say it looks very good for a classic HTML site, the site and especially the tables aren't broken, the text is just too small - have a look at my page, it is broken on mobiles, but it doesn't bother me because the content is for computer users (with a resolution of 1024*600 at least) and it will never be possible to put this kind of design into a responsive design. I also already designed a small HTML page with responsive design, but it doesn't have so many columns in its tables and doesn't have such a menu at the top and on the left side.
Keep in mind that with the topic (BIOSes for old motherboards) there are also users with old computers, old browsers and JavaScript disabled who want to access your site - this is easily possible, especially with the HTTP version, but also with the HTTPS version and a suitable browser. I wouldn't break this.
You don't need a fixed menu, but even this is possible with CSS...just start with a simple menu and then go further, if you want to.
I'm very sure, I forgot a lot...just let me know if you're interested into "keep pure HTML". 😉
kind regards
soggi
Vintage BIOSes, firmware, drivers, tools, manuals and (3dfx) game patches -> soggi's BIOS & Firmware Page
soggi.org on Twitter - inactive at the moment