Nuclear Electric space tug with Fusion-assisted Exhaust Heating

I am looking at advanced rocket possibilities for getting delta-V once in space (not taking off from any planet or moon).
The page http://spacetethers.com/moon-l5 has my thoughts on how we are probably going to see a huge
increase in space activity and this will drive a much bigger justification for some high
ISP space tug.

I think nuclear fission modules are the best way to get lots of power in minimal weight in space.
I think using electricity to do as much fusion as you can is the best way to get lots of
energy into exhaust going out the back of your rocket.
So fission for electricity and fusion as part of the rocket engine makes the most sense to me.

The "direct fusion drive" idea seems like a good way to get extra thrust when you have a
source of electricity but I worry that their plan to get net positive energy from fusion
will fail due to the "fusion is the energy of the future and always will be" problem.
It would seem the general approach would have a much higher chance of success if
it did not require net positive energy.   So it feels like having a fission reactor
and a "direct fusion drive" together might avoid that very hard requirement.

So the fusion is just getting more "bang for our buck of electricity" in our rocket exhaust,
not the source of power.  Just a more efficient use of the electricity and reaction mass.
If fusion allowed you to get 4 times the exhaust velocity and 2 times the momentum
from your reaction mass, it would be a huge win, even if it did not contribute
to making "usable energy".

If we had a production rocket that even made 20% more energy in the ehaust from fusion that would be a win.
Over time the development could keep increasing this percentage.   This sort of situation
where engineers can keep working on something and making it better over the years can work really well.
It could be the best way to eventually get "net positive energy from fusion" really.

Please look at a space tug design along the above lines to move 200,000 Kg from LEO to L5 in a month.

What scale of nuclear-electric power would make sense for this?
What sort of mass for the power plant and the fusion-enhanced thruster?
What is the ratio of energy in the exhaust with fusion to energy in the exhaust without fusion?
What sort of ISP?
What sort of thrust levels?
What sort of time to go LEO to L5 would you expect?
What sort of time to go back empty from L5 to LEO?
If the same design were used to carry 600,000 Kg from LEO to L5 in one trip how long would it take?
Imagine Elon Musk team and funding, how many years till something like this could fly in space?

Please output your answer in html so I can put it on a website.