No. They both connect opposing clauses, making an although/but combo into a double negative. You might be able to, but it doesn't make as much sense.
It was crude, but refined, although it had an air of vulgarity to it...
Yes, you can use both "can" and "may" in the same sentence. For example, "You can call me if you may need help with your homework."
although the two words are different, the semantics are the same.
Although love as a feeling is not palpable, its object almost always is.
They were happy although they were poor.
yes
Although it's raining, we can still go out to play.
Although it is raining, I decided to walk outside anyway.
Although difficult, it's not impossible.
You use he or she when you already have referred to a person in a sentence before, or earlier in the same sentence.
It was steaming out side although the girl insisted on wearing jeans and two jackets.
Although difficult, the problems seemed surmountable.
although the two people use different techniques they manage to coexist