I think you've done about the best you could. Keep the bark on, seal the ends (varnish, wax or PVA glue generally work well for this) and keep them out of the sun and rain. Unless you know where each piece is going, keep it at maximum size, this will allow you lose some wood to cracking and still end up with usable pieces.
Once you have a better idea of pieces you want to make, rough turn them to about double the final wall size, and let them dry out some more inside the house. This will cause some warping, but you should have a limited number of failures due to cracks. Buy yourself a moisture meter, they are quite affordable. For boxes (where the lid should fit nicely) you will want to have moisture content below 10%, otherwise you'll find that the day after you finish turned a piece the lid won't fit any longer. For other items you can work with slightly higher moisture contents, up to about 14%, but be aware that there will be some movement in the piece afterwards.
The wood in the picture is definitely laburnum, a good wood for turning, as it is quite hard and generally has nice grain. The downside is that laburnum is toxic, so make sure you don't ingest any of it. And don't use it for anything that comes into contact with food.