TBH, you don’t need to worry about site speed as much as you think you need to.
The reason is that there are limited things that you can really do or should do.
I’ll tell you why. CSS, HTML, Javascript optimization are all made by your theme that you’ve picked. If you make customizations or changes now, it will be very hard to maintain and if/when the theme updates that may mess with how your site functions.
If you have developer go into the site they definitely can make a lot of optimizations, but it opens you up to issues down the road with maintenance and changes.
The best thing you can do is optimize your images by compressing them and serving the right size of the images to the right device size. Then just removing any unnecessary apps that your server may use. Look particularly for those that install code in your theme, because those are typically blocking your site from being functional until that script loads.
Otherwise, I personally don’t recommend doing too much more unless you have a web developer on hand.
Cheers,