Avgas at airports is nearly always 100LL (100 octane low lead) That doesn't have alcohol but it does have a fair bit of lead in spite of its low lead...
Re board length a rule of thumb I've seen says board length= total jointer bed times 1.5. I have done twice the jointer beds but wouldn't want to go...
What I've read about 4K is that it makes a difference on larger displays, generally 50" and up. There is another technology called High Dynamic Range...