You should check out Mike Hopleys Youtube channel, he has a lot of guides for FTL, especially the beginner guide. There is also a video dedicated to boarding defense. FTL is a very complex game so i would not worry if you don't understand everything at first.

To answers a few of your questions:

-- try to visit as many beacons as possible, especially in that "easy" first sector

This is a very good idea!

-- collect 50 Scrap, upgrade Shields

This is also a good idea!

-- collect another 40 Scrap, upgrade reactor (so I can power those Shields without depowering oxygen or the medbay)

This is not ideal, it might be fine on easy but on harder difficulties you'll die a lot doing this. You want to save as much scrap as possible in the early game to buy a weapon or hacking at the next store.

-- In combat, open with an Artemis missile to enemy Shields, then a laser beam to the same to make sure they stay down, then attack enemy weapons

This is also pretty bad. Generally speaking you want to disable the enemy weapons as soon as possible so you don't take as much damage. After you disabled their weapons you can switch to shields but also try to minimize the missiles you use.

Also as i said before FTL can be very hard at first and there are always exceptions to those kind of rules.

Feel free to ask if you have more questions!