Golly, Brumbull, your head must be bursting with ideas! Quite a few current threads were started by you! Not that I'm criticising, I promise - I'm enjoying them.
Successes - finding out which plants are tough enough to survive my ministrations and planting them! I love hardy perennials. In a sink or swim situation, they usually swim.
Failures - I can't grow rhododendrons and azaleas (soil is neutral and I have always failed with them) and roses struggle in this wet area. I once planted bearded irises in the shade and too deep, with predictable results. No flowers. It took me a long time to realise how greedy and thirsty roses and clematis are. Then there's...err... how long have you got?