1. LE builds with Alsa and Pulse; the latter is only used for BT audio (streaming to LE from a phone or other BT device) and Alsa is used for Kodi. As pulse is included in the image you can always go fiddle with it to enable pulse output in Kodi .. but sounds like this is not desirable.
2. It would depend on the capabilities of the enclosures/firmware being used in them. Most drives will power down when not used. Some drives have shitty firmware that needs manual forcing so there's no single answer. If you need to force it with a script in other distros it may need to be forced in LE as well.
3. No. LE is built to run Kodi only, there is no "Desktop" environment. You also cannot tinker with drivers from within LE itself (there are no build tools) but you can create your own custom LE image with changes using our very simple to learn build-system (on GitHub).
4. We run a newer <everything> code stack than other distros which sometimes brings improvements (due to newer code) but otherwise no idea.