Have a look at the video at the bottom of this page:
http://rc.noalia.fr/boats/barge/20150227This is a Springer tug around 4kg and 450mm length using a single 45mm prop in a Kort Nozzle pushing a 1200mm x 400mm barge that weighs around 25kg ballasted. Total around 29kg and 1650mm length. See what I mean about 2 x 50mm? Having said that if you turn the 50mm slowly enough then they would work just fine but they are not required.
Keeping to the same blog have a read about the development of the Springer used here. It is well written and should help give you a few ideas. It is a good example for you to consider.
I doubt that you will think that you need this much power for a relatively small light barge but opinions vary.
Calimero is a member of this forum.
The bow thruster will help manouverability. I recommend this Ministeve type which work so much better than those that you can buy.
http://www.modelboatmayhem.co.uk/forum/index.php/topic,20067.msg193914.html#msg193914Come back with your thoughts.