Thanks for all the advice.
I know about the Smogon sets but competitive sets are not always practical in-game (from my own personal experience). Flare blitz has nice power but taking 1/3 of the opposing Pokemon's HP isn't very practical since I'll have to rely on lots of healing after trainer/wild/gym battles (time consuming and excessive use of items).
The breeding suggestions are good and were considered but I don't feel that it's worth all the effort when I probably wont play the game much after I finish it.
Reason why I opted out of Hydro Pump is cause of the 5 pp (8 max... except I don't have any PP-ups or PP-maxes) so again not as practical in-game.
Sludgebomb on Gengar is a nice STAB move but does it seem like I benefit more from the coverage of T-bolt or Giga Drain? (Giga Drain would also be more reliable recovery than Dream Eater).
And yes I considered the Ambi set but I decided to use him mainly for Pickup. I will replace him with someone else later on.