I expect lilly pads will just gum up the inlet on a jet.
This boat is reportedly quite immune to weeds: http://www.streamdancer.com/
It uses auger type props. These avoid blades that trap weeds. There are amphibious vehicles based on the same concept; been around for a long time: http://web.ics.purdue.edu/~warnerd/i...s/Page1421.htm
One way to beat the weeds is to do what is done in the swamps. Avoid water propulsion and use air. Problem with this is you need a large prop to do anything useful. Something like 2ft diameter on a 10ft boat would get you moving but efficiency only 40%.
The electric RC stuff you can get for peanuts (or maybe a little more) these days are very powerful. This motor is bigger than you need for power but is the sort of size needed to swing a big prop unless you set up gearing - why bother though: http://www.hobbycity.com/hobbycity/s...ner_(Eq._52-20
Hobbycity have some large CF blades but I have not looked at how they mount. Large RC copter blades would be close to ideal. A couple of kg of thrust is all you need: http://www.hobbycity.com/hobbycity/s...Fiber_Z-Weave_
There are Bolly props made for large models but these get expensive: http://www.bolly.com.au/models/glasstwo.html
The 24X8 would do something useful at reasonable efficiency. Need to mesh to guard it.
The fundamentals of a water thruster work against your little pump idea being very efficient. If you could set it up to avoid the inlet fouling you have to have quite large power to generate usable thrust. As a first approximation the ideal power as a function of thrust can be determined as:
Power = (4/pi/9/rho)^0.5 x Thrust^(3/2)/D in Watts
You will require a thrust of 20N (say 4.5lbf) to do something useful. Rho is 1000kg/Cu.m. D has to be in metres so for a 1" nozzle say 0.025m. Under these conditions the ideal power is 42W. You could double this by the time you account for plumbing and pump losses. A 6" pump would need to spin at 800rpm to do the job. Something off-the-shelf like this would be adequate: http://www.boatshop.com.au/prod19.htm
You would need to nozzle it somewhat to get the best result but it is the sort of size required. Anything smaller would be literally pissing into the wind. Efficiency would be similar to the air prop.