That the smaller plant died, and that you were surprised at how small the root mass was, is probably a wake-up notice that there is something amiss. Most likely, it would be over-watering and/or an accumulation of solubles salts in the soil - both very common in plants grown indoors in containers.

The larger plant probably grew so well because (from a hydrologic perspective) setting the pot on the ground turned it into a small raised bed. IOW - water behaved in the pot in the same way it would in gardens & beds - the earth acts as a giant wick, 'pulling' excess water, and accumulating salts, from the container. The roots that 'ran' from the container also provided the plant with nutrients and a healthier environment not found within the confines of the container.

I draw distinct delineation between repotting and potting up. What I WOULD do at this time, is pot up a size if the roots are very tight, then wait until Jun to do a full repot, which includes a soil change. At that time, I would be sure I was using a durable soil that drains well & will retain those drainage characteristics for the full interval between repots. There are lots of discussions about soils for container growing on this and the Container Gardening forum. Join one, like this 6 year old thread
to learn more. Your choice of soil is extremely important to your effort:reward quotient.

As far as growing tips, these fit virtually all plants we grow in containers and are offered in what I feel are their order of importance.

Choose a soil that ensures good drainage and aeration fir the entire interval between repots.
Learn correct watering habits.
Learn to fertilize with a good, soluble fertilizer so your fertilizing habits mesh favorably with your soil and watering habits.
Make sure light conditions and temperature are as favorable as possible.
If you can manage to get these few principles under your belt, there are precious few plants you can't grow with excellent success. I should mention insects - that you learn to identify and deal with them, but the likelihood of that probability is greatly reduced if you're good at supplying the other cultural needs already outlined.

Propagation is a funny thing. It's easiest when most (house)plants are full of energy in mid-late summer. Plants also carry this energy into fall and early winter, but you generally get a lot of root growth and little foliage during that period. For that reason, soil and watering habits are more critical, with a lot of plants succumbing to root issues related to saturated soils. If you DO try to propagate now, be patient and be very careful not to over-water. Use a highly aerated medium like screened Turface, screened perlite, or screened calcined diatomaceous earth.

Al