Single target again, I believe yes. AOE, no, even if the tank can work with ISS heals in that area (even with exalted), you will not have enough DPS to kill mobs fast enough and you will probably end up with no mp on ISS.
I cannot give you great advice on 3member parties as my main is tank and all the investments go there, so I do not have a DD to actually kill. Only thing that has worked wonders with me and friends, is maestro-iss, evis-iss, these two pairs can do wonders even with exalted gear.
My proposal remains the same, find a helpful PVE clan. From there, you can find all the help you will need. Easy instances, easy dailies and you will eventually build up. Keep doing Storm Isle, PI, Crisis, IT at least per day. You might get lucky with the boxes or get some scrolls for investment.
Unfortunately the game is playable easily till 105. Then, the difficulty skyrockets, you have to play in group unless overgeared. Only toons that can effectively play solo (or duo with ISS) with exalted gear are evis and maestros (106+), but its a very slow process and has become very difficult after the latest update (mobs have less def but more atk).