Farseer guide and fortune questions

Look around on the internet and saw some topics related to the psychic powers but none on this situation. I ran into a list where a farseer was in a tau squad casting fortune and guide on himself so the squad can benefit from it. The farseer was the only eldar model in the squad and he was able to re-roll his saves and hits even while overwatching. A couple questions about this:

1. Can the farseer target himself since the codex says "Nominate one Eldar unit with a model within 6" of the farseer."

2. If he is able to cast it on himself will the tau squad still be able to benefit from it even though they are not eldar?

3. Does guide carry over to overwatch, allowing him to twin-link his shots when im charging that unit?

4. Just to make sure, the last sentence of Fortune says "This unit re-rolls saves it makes until the start of the next eldar turn." does that mean if I had an eldar army his fortune would end on my turn?

Thank you for reading this!

For #1&2 i would check the FAQ but I would probably guess yeah it would work for the unit b/c of them being battle brothers.
For #3 yes it carries over to over-watch u just need 6's to hit
For #4 it means the power last for one whole game turn from when it is cast so ur turn and your opponents then ends on your next turn
Hope this helps and answered your questions

Thanks for the reply!