A scarf joint is used to disguise the joining of two pieces of trim in a straight line. That is the 30 or 45 degree miter folks mentioned. I use 45 degree because it is easier to set on my miter saw. There is a right way and a not so right way to use a scarf joint. The right way is to have the closed end---the end with the miter cut so the inside of the trim cannot be seen----as opposed to the mating piece, which is cut so the trim inside can be seen-----is placed so the line of sight from the entrance to the room looks over the joint instead of into it. Get a book from the local home improvement store---best $10 or so you can spend to learn that and more. Like using painters putty to fill nail holes in painted trim.

Correct, what you really need to know is the BTU/hr the thing puts out. Fortunately with an electric resistance heater (as these are), there's a direct correspondence between the wattage of the heater and the output. As pointed out, the 1300 watts you need is pretty much the top end of what you can legitimately get out of a portable (plug in heater). Yes, the heater will run only as much as it takes to get the room up to the set temperature. The one advantage of these electric baseboards is they typically respond pretty fast (they get hot as soon as they turn on). There's also no real disadvantage of putting one a bit oversized in. It will just shut off faster even though it's consuming more power as it is running. This is in stark contrast to a heat pump or even conventional furnaces that lose efficiency when you run them oversized.

I agree with you. That looks awful! If the skirt is wide enough to accept base and shoe, and you're planning to have base and shoe on each level. Base should also be ran on the skirt. However, if the skirt is just wide enough for base, and you still plan on having base and shoe on each level. Then the base should be run like the pictures I'm posting. You'll notice the skirt isn't wide enough to run both base and shoe. So on the landing, the shoe is terminated by using a mitered return. Shoe ending into skirt board. No shoe, just base. Base is not cut flush with wall. This is a compound mitered return where it ends so the profile of base wraps back to wall. Example of a shoe ending with a mitered return.

Not a miter box--a 45-degree angle on a table saw! Yes, ripping a clean angle would still give a simple,modern look and not make me lose my mind. Too late for avoiding some rip-outs, though! Do you really want to dust your baseboards every single week? In every room of the house? I don't. Once a month, sure. That's why I was glad to get raised panel, not shaker doors. I shouldn't NEED to dust my doors, for heaven's sake. Shaker anything I now avoid. I never would have dreamt the difference.