When I played Prophecies for the first time it was hard but henchable as long as you were part monk and could res the henchies when you go with henchies its not if they are going to die but when. Ideally Rebirth if possible.
I think when I was leveling up my warrior I henched everything except for thirsty river (The henchies dont pack enough damage or anticasting skills to stop the 2 healer bosses from healing each other). Its possible to do almost everything with henchies but just takes a lot of work and will be much much quicker if you can find a good group though good groups are harder and harder to find these days.
If you do consider getting another chapter get nightfall for the heroes they will make the other chapters much much easier being able to have 3 extra level 20s around with builds that you can control if you got the skill unlocks. Also if things get really tough for most missions youll be fine by overloading on monks/healers as long as you bring enough damage it just take forever but it will get things done.
One comment i have to make if you plan on getting all 3 GWs just know that the endgame content is based around PvP unless you want to farm just for the sake of being rich and enjoying the farming. Either way youll get the most out of guildwars by playing with people you enjoy playing with otherwise its just an endless grind.
Guildwiki is going to be your best friend its like the thottbot of guildwars
http://gw.gamewikis.org/wiki/Main_Page .
I play wow too these days but playing guildwars right now till BC comes out kind of pointless when you know all the gear you put tons of hours of raiding getting will be reaplced by better AH greens in 2 months.