I hope there isnt a topic covering the questions i have. if there is i didnt find it.
i got a few question concerning summoning and killing bosses with a party.
-1: At what level can you start summoning bosses(im currently ~lvl 43
-2: do you really need a party or can you somehow do it alone?
-3: can it be enough to be in a party with a teammate who is offline?
-4: is it rewarding or should i better keep questing?
hope someone can help me with these questions 

ah to bad. i usually enjoy playing solo some time and thought it might be fun killing some bosses alone.