The safelight can stay on all the time. But you should test it to see if it fogs your paper. take a piece of the paper you use, a small piece will do, lay a coin on it and set it on your easel with only the safelight on. give it a minute or two and process it . If there's a darkening of the area around the coin the light isn't completely safe and needs to be changed to a different color or moved further away
Two armed easels are meant to have the paper pushed to the upper left hand corner and the arms adjusted to the print size you want. You will need to trim the paper if you're printing smaller sizes. A four blade easel will allow you to make more even borders though.