Newbie needs help with a lights project

I am going to be hooking up the 40 LED lights (Christmas tree type) powered by 3 1.5v AA batteries. I am ok with basic soldering.

The whole thing is a permanent fixture, the board, accelerometer and the batteries will be concealed so only the lights will be showing.
Only doing this as a one off so it doesn't have to look too pretty, just needs to work.

If you can guide me on what you think I should get to start with it would be really appreciated, I just dont want to buy something which will end up being totally the wrong thing to get.

Sorry for being so rubbish at all this, just very very new at this.