Legal formation?
 

Is it legal for the offense to have eight men on the line of scrimage? If so, does that cause six of them to be inellegible? Should those six wear inelligible numbers?

Yes.

Yes. An offensive lineman is ineligible anytime he is covered by an end.

Not necessarily. Barring scrimminage kick formations, at least 5 needs to have 50-79.

The only numbering restriction pertaining to ineligible numbers requires 5 linemen to be ineligible by number. Having more than 5 ineligible by position does not change that requirement in any way.

Speaking NFHS:

Only 5 need to wear 50-79 on the line and they can actually be on the ends. They are ineligible by number.

These rules are completely different in the NFL.

So if A55 is lined up as a wide receiver and is on the end of the line, he is ineligible to go down field. If he goes down field and a forward pass is made, we have ineligible downfield. If he goes down field and catches a forward pass, we have illegal touching and ineligible down field. B would probably take the illegal touching, as it is LOD.

Correct?

Nearly correct. 'Eligibility' pertains to being a receiver, not "going downfield." On a screen pass, for example, any player can "go downfield."

A55 is an ineligible receiver by number, and your account of the fouls and penalties is all correct (for NFHS at least).

What if the pass crosses the neutral zone?

Same for NCAA. New NCAA requirement from about 2008 or 2009 has no requirement on line, but no more than 4 in backfield. 5 on line is legal since 5 must be wearing 50-79.

Cobra: by screen pass, he means pass caught behind line. Once pass crosses line, you get into ineligibles (either by number or position) downfield.

Then I wouldn't call it a screen pass. :p