Cotoneaster is a great bonsai species but don't listen to your gut. Cascade may look exciting and relatively easy but getting it right turns out to be really hard and even harder to maintain long term as most plants are apical dominant so the lowest part of a cascade is always weak. Good pruning and care is even more essential with cascade style.
You could continue to develop the long, leaning trunk it has now and just position branches to compliment that.
You could also work towards an informal upright style with it. Just chop the trunk above the strong, upright branch just inside the pot rim to change the trunk line to a more upright style. Repositioning the trunk at the next repot to change the current trunk angle is also possible.
Crepe myrtle is exceedingly good at budding from older, bare wood. I would probably chop all the trunks way, way back and start developing the branching where it will be useful. CM chop can be done almost any time of year but if you want to see flowers then wait till after flowering.
The maple is a large leaf type so not really desirable for bonsai. You could use it to practice pruning and repotting but I don't really see a high quality bonsai future for that one.
Please update your profile to include a location because many things in bonsai are tied to weather and climate. You'll get much better advice for your circumstances if we know where you are.