About time to go outside

It looks like the Iowa weather is finally cooperating and I can send Li-Wah (I named her after the Chinese restaurant next to the Asian grocery) outside soon. Last year, when she was outside, I had no idea what kind of turtle she was and didn’t have a nice setup. So this year, I’d like to at least make her area a little nicer. Currently, she has a 4’x’8x 20″d enclosure with a hinged top wooden frame lid (chicken wire within the lid frame, wooden sides all around). Her water tub is teeny, I think 2×4 ft. and only 8 inches deep (It’s a concrete mixing tub). She has a little carport on each end and she likes to hide under the carports rather than sit out in the sun (probably fear of raccoons (-;). My husband gave her cypress bark mulch substrate last year, it’s easy to change, though. If anyone has any suggestions, I’m wondering 1-when is it warm enough to go out for her? We’ve got 50s and 60 degrees now, but that’s downright tropical compared to what our past few months have been. 2-how big should I make her water/pond? I don’t know the first thing about pond filters or pumps. What’s the difference? I don’t want to make a HUGE enclosure, so if we could keep it close to the size of her current one, that would be great. 3-does she need sand or some other substrate instead? Does she need plants? 4-Any other ideas? Thanks! I’m going off to Minneapolis briefly and hope to scout out some Asian markets. Rowena