That's not a probably, just a maybe. Spinal damage does not necessarily mean impotence. There are plenty of wheel-chair bound men whose male equipment works just fine.
His mentor said that wouldn't happen to Bran.
Good point! Accepting your father was a madman is one thing, marrying his killer is another matter entirely.
Littlefinger isn't going to take Sansa's rejection lying down. I won't be surprised if he sides with Cersei against Jon and Sansa in the beginning of next season. Maybe he'll marry Cersei in a plot to steal the crown from her and become king himself.
He barely even got to know his wife before they threw him in a cell. I don't doubt that he feels a certain fondness for her, but I suspect that he was more concerned with his prospective child's survival.
Only three people hated him, and two of them are dead. As for the third, she too will be dead by the time Dany takes the throne, because there will be no other way for Dany to take the Iron Throne except over Cersei's dead body. So that's not a strike against him.
Euron has a bigger fleet than Dany, and he may well have a Dragon Horn that can deal with Dany's dragons. So it's not impossible that he may put Dany in a position where she has no choice but to accept his marriage proposal. If that occurs, I expect her to find a way out of it ASAP however.
Now that Cersei has blown up the Sept of Balor, the seat of the Church of the Seven in King's Landing, along with the High Sparrow and his army of fanatical goons, I don't think the Church is in any shape to give Dany a hard time.