Good for you! Your paintings are great. I agree that painting is a fun way to play. Unfortunately I can't help much when it comes to acrylics. I'm mostly a watercolour, ink, and digital gal. But what I do know is that they dry super fast, so while you don't have the unlimited blending options you get with oils, you do get is the ability to paint over things you don't like. (Ink and watercolour are not particularly forgiving in this way!). You can build up dimension by layering colours, too.
My advice to beginning painters in general would be to stick to no more than three colours, and mix what you need. Try not to use too much black. Pay attention to where the light is coming from -- a single light source makes things easier. Draw and paint from life whenever you can.