I did my our barn once but I didnt have to sand.It went easier than I thought.I did as far up as I could reach he did second floor.When painters worked on our house they used orbit sanders little palm sized ,but our boards were rough cedar on barn.

I just had my 1906 house professionally painted last year. The painters used the orbital type sanders (this will leave marks). If the house has lead paint, you need to protect yourself and the immediate surroundings from the dust. Masks are obligatory, and the painters put dropcloths on the ground and hung a plastic sheet over the whole side of the house they were sanding. They worked under the sheet and collected the dust at the end of each day and carted it away in buckets. The town I live in has regulations about sanding old houses, and some of the surrounding towns have truly draconian regulations. Check with your local municipality, but most importantly: protect yourself with appropriate clothing and breathing apparatus. even if you don't have lead paint, a mask should be worn while sanding.

Nora

If you actually have to get the paint *off* rather than just smoothing it out, a heat gun makes a lot less dust than a belt sander & is lighter and easier to use. Below IIRC 1000 degrees it doesn't vaporise the lead. Lead is a big issue if your house is before about, uh, 1975.

Repairing rotten posts and window parts - epoxy - thin stuff to soak into the rotten parts to stabilise them, and thick stuff to fill the holes. West System and Abatron are well known makers. Good article here:
http://www.hereandthere.org/oldhouse/fixing-decayed-wood.htm

Here is a link that might be useful: fixing decayed wood

If the paint is adhering well, you really don't need to take it completely off. It's doing just fine as-is. Scrape down (spritzing with water to cut down on dust) just to intact paint, whatever layer that may be, then feather out the edges by wet sanding--better than dry sanding when you're talking about possibility of lead paint.

I second the recommendation for a heat gun rather than a sander. Just use caution that you don't scorch the wood, and keep an eye on it to make sure it isn't flat-out burning. One of my old instructors had a video of a house that had caught fire while its painting crew, who had used heat guns but not carefully, was out to lunch.

Also, take the advice of others here and wear appropriate masks/respirators. They really do make a huge difference in your comfort level, and in your safety level as well.

We tired a product called Peel Bond which we saw at a Sherwin Williams store. Eliminates a lot of the sanding. We used it to prime an old painted house we did. The stuff is high build and you can build up the low areas where paint has peeled. It also is a bonder which helps keep the topcoat looking good. I'd google the name to find it.