Hi LaSargenta,
Since I am one of the few BWCA folks on this board, perhaps I should try to respond to your query. Lizz is a favorite entry point of ours, and you have chosen a good trip for you and your ten-year-old. Poplar could be a problem in the wind, but I would say it isn't usually a big deal. Any larger lake can be a challenge if the wind kicks up, and the best advice would be to get on the lake early in the day. At least that is the best advice for most days.

You need to be sure that you are looking at BWCA maps. There is no campsite on Lizz. Lizz is just a small entry lake and then you portage into Caribou. Your first opportunity for a campsite would be on Caribou.
Caribou is a lovely lake and has some nice campsites. If you base-camp there, you will enjoy it, I am sure. But if you decide to go on, Horseshoe is a neat lake, too. There are some nice campsites there, and it is often a good place to see moose. We have had several moose sightings on Horseshoe on different trips. Vista is also a beautiful lake and the campsite on the southern end is first-class (but hard to find vacant.)
How about staying on Horseshoe and making a day trip over to Gaskin?? Just another possibility? Gaskin also has some nice campsites, and some lovely scenery. We don't fish, so I can't give guidance about fishing in these lakes.
I am a bit puzzled by your comments about going out at Jake and Morgan. Yes, you can do a one-way trip. But you would have to have someone pick you up at your final destination, or spot a vehicle there. This would have to be a decision you made before your trip, not "IF the pixie is hooked on canoeing and IF the portages go well". And, frankly, I think if it is just you and the ten-year-old, that might be a rather ambitious plan for the first time in so many years. Just my two cents.
No matter how you do it, you have chosen a very beautiful part of the BWCA, and one where you should see some wildlife and have a great time! Have a fun trip!