1. If you want to improve page load speed you need to buy a HTTPS certificate so you are not limited to HTTP/1.1. Multiplexing in HTTP/2 is important for getting sites to load fast.
2. You can set the HiddenServiceExportCircuitID configuration to pass the circuit id to your web server for telemetry or anti abuse purposes. Otherwise your logs will say that all users are coming from the same IP.
Which raises the question: why not just trust self-signed certificates on onion services? From my brief look it seems to be because the Tor project views the primary purposes of HTTPS on onion services to be other things rather than just http/2 support: http/2 isn't even mentioned on their page about https for onion services (https://community.torproject.org/onion-services/advanced/htt...). Unfortunate.
Trying to push hidden services to stay on HTTP is going against what the rest of the web is doing and as a minority of web traffic it really should be aligned to the rest of the web and also require HTTPS. Yes, it's technically wasteful, but reduces both work and security risk by keeping security models aligned with the rest of the web.