Q1) I never have sided with Bohdi before so does it play out normal other then then quest to get Leina? Meaning that is the only thing that is altered?

Q2) Is it correct to conclude that if you don't pick the correct response, that you will never be able to get Leina later in the game?

Q3) If I went directly to Spellhold to get Immy is it still possible to go to Ulcaster and end up back at spellhold or in Brynnlaw?

yes
For Bodhi's second quest she gives you the option of doing an "evil" quest or a noble quest. Do the evil quest. Even though you choose evil you don't have to commit the murder she demands.



Yes, you must choose the evil option.

Hrothgar will leave your party in 15 days of game time, and you won't be able to play NeJ further.