The “optimizations” regarding loading CSS and fonts your mention are actually pretty insignificant these days. All together, that load would be likely is less than 100K or 200K – not much. Maybe a few years ago it mattered, but it shouldn’t now. Things like that that used to matter just don’t any more. I know it has been hard for me to change my thinking on that, given so many years of experience where it did matter, but internet bandwidth and server speed are just so much faster these days that it is just not really worth the effort for such tiny improvements.
Perhaps if your hosting company is behind the times as far as server performance, or if your viewer base is mostly in parts of the world with limited internet access or largely rural with slower internet speeds, it could still matter.
Serving images can be a different story – sort of. If you are serving the typical US or EU customer base, it is still shouldn’t make much difference.
But how images are served these days is a bit beyond whatever theme you use, but instead relies on either how WP is configured, or what image helper plugins you use, or which global content caching service you used (e.g., Cloudflare) you use.
Your time will be much better spent optimizing those latter things rather than trying to tweak a few CSS files or font files. That content is all together less than even a medium sized image.
Additional note: some of the “optimization” tools that exist today may show what seem to be significcant performance issues, but do remember that most of those services may have a lower tier free service, but they really want to sell you their higher end services, or are now free because they really don’t serve as much of a useful service as they might have a few years back. They want you to believe you can improve things, but that is just not as true anymore.