1. Minify JavaScript: I can’t do it because when I do it always causes bad behaviors in the scripts.
If you developed the theme then you should use the webpack for your JavaScript and CSS files. That will automatically take care of minify the js and css on both sides ( development and production ).
2. Leverage browser caching: I’m not sure how to do that… Maybe in htaccess?
Yes, .htaccess trick will help you.
3. Defer parsing of JavaScript
1.0MiB of JavaScript is parsed during initial page load. Is it a lot?
I’m not sure how to do because the biggest js are the one coming from plugins, like for example revolution slider. If it doesn’t load first, then the slideshow won’t appear…
This is something that you can’t handle. This is the biggest issue comes with most of the plugins.
4. Optimize images: I will try to do it but I need a good tool and I must admit all the tools I tested were not good for image quality. And GTmetrix says I will gain 65kb which is not much.
There are many online tools to compress images such as https://compressjpeg.com/
5. Combine images using CSS sprites
I can do that too but I have D for this one so it’s not that bad.
If you can do this then you should.
And finally, if the internal pages take more time to load the site, then there are two possible issues.
1. Make sure to not use too many plugins for your site.
2. It is the bandwidth issue provided by your server.
But before changing your host, I recommend you install this plugin to identify if it because of any plugin or your server.
https://www.ads-software.com/plugins/query-monitor/
Hope this will help you.