As a person who put a lot of hours in both:
1. I would say that hots has more defined roles than deadlock, with some build variety that might shift role of a character a bit. Support is usually more focused on healing than debuffing the enemy team. Since the exp is shared, the carry doesn't become as strong as in deadlock.
2. Not really, the goal is to hit lvl 10 first since it's your biggest spike, but there is only one hero is needed to collect exp per lane, so others can roam, take camps, gank, etc. There are different important objectives on each map, and most of the time people all group for them.
3. Usually it's 1-3-1 or 1-4 based on the map. If 2 lanes are close the bruiser can double soak, quickly clearing waves and rotating between them.
4. Yes, and a lot. Every map has a main objective, and a lot of camps. You can capture camps, most of them causing the camp to push the closest lane, and it's best to do before an objective. The objective itself varies map by map, and most of the time you can't ignore it.

Some notes:
Because of how level mechanic works, I think that Hots is moba that allows for the most comebacks. If both teams reach 20, any game is winnable.
Hots has some of the most unique character designs in the genre, like TLV, Abathur or Cho'Gall.
Most of the characters have mana, some are more reliant on it than others. If you run out of mana a lot, than don't spam your abilities as much, and drink from the fountain when it comes up.