1. Highlighting is a known Qt issue - no fix. You just have to workaround as you do, or highlight a larger area.
2. Spacing should be done by styles, but in any case the won't be added. The html from Book View is under control of Qt not Sigil. If you really wanted it, you could use Find & Replace.
3. Clicking the include box does not delete the entry. Click on the Show TOC Items only so its unchecked - then you'll see all your headings.
4. Hmmm, it should allow you to browse to any location to pick your program. At least on linux.
5. Can look at adding these. The entries there were the basic html entities - been wondering if anyone wanted others added