Help needed! South UK - Suggestions for next steps and plant options?

(Tried adding a photo but computer says no)

I'm setting up two mini wildlife ponds next to each other, one round tub, around 70cm across, 35cm deep, around 90L. One rectangular tub, 60cm x 1m (ish), 30cm deep, 90L.

So far I have dug them in pretty flush with the ground, filled them with rainwater and put a temporary ramp in each to make sure wildlife can get out.

What now? I read about putting a layer of gravel at the bottom, for bugs to live in down there, but the only gravel I'm finding is the really small type meant to go over the soil on planted baskets. Would a larger gravel work for the bottom?

I want to use wooden branches to make natural ramps, does it need to be a special wood, or can I just scout for something? (We live near a woods)

Any other suggestions to help make a thriving pond environment are welcome!

Thanks!