I moulded all of the skirtings in my house from planed timber, because moulded skirtings then were expensive and I had the tools to do the job, but i let the wood acclimatise to the room beforehand.
What I did was to stack the timber in the room, but with thin strips of batten between each board to allow airflow.
I weighted the top board and left the timber for a week in the room.
I did the same with several softwood panelled doors too.
These were then stable enough to be machined and fitted soon after.
Some bowed a little and the very bad stuff needed planing before fixing.
All painting occurred after fixing, filling and final sanding.
Since then, I've seen primed MDF skirting, which looks like an easy, but expensive solution to real timber, saving a lot of work painting.
Personally, I don't like stained softwood - it looks like what it is: a cheap and nasty imitation of hardwood.
Also, quality finishing hardwood is not easy and most attempts I've seen really let down the beautiful timber beneath. You really need to spray it to get the best finish. This material also requires a very high standard of joinery and very fine sanding/preparation.
On softwood, it's Satinwood finish every time for me, but each to their own!