I'm looking to purchase the sun dolphin pro 120, and needed to if it'd get around okay with a 55lb transom trolling motor, or if it needs one of those big outboard motors? I'm on a budget so if the outboard motor isn't a necessity I'd do without it. 

Use what ever is in your budget.  A trolling motor will work just fine.  I'd stick with the biggest thrust that works off a single battery.

A 55 lb thrust TM gets my 10 foot Basshunter cruising at about 3.2 mph.  Plenty fast for the small lakes I fish.

okay thanks guys

 

 

It definitely depends on how far you're planning to go. If you're only going to be fishing a small lake/pond or are ok with only fishing a small section of lake a tm will be just fine.