Spend more time than you think is reasonable learning how to stop by footbraking. The slightest incline is quickly going to bring you up to speeds that WILL cause you to fall if you try to jump off and run it out.
My advice would be to start with the wheels chocked and just get used to moving your weight to your front foot and then lifting your back foot off the board, touch the ground in a completely controlled manner, and then putting your foot back on the board.
Once your comfortable with that you can start doing the same thing with some forward movement and very gradually build up the speed.
Being confident in stopping will make everything else you learn so much easier.
Also, maybe consider a cruiser rather than a longboard for your first board. I can use my cruiser to go the shops and clip it to backpack when I’m actually in the shop. It helps to spend as much time as possible on the board so anything that encourages you to use it for short trips is a good thing.