1) Powder manufacturers data is on line and may give you the COL they used in testing. Comparing that to bullets listed in the powder mfg data and your books can help guide you to a COL to begin load development. Also, a time-tested approach that works is to call Hornady. They can give you a test COL for your chosen powder.
2) If you want to load through the magazine, measure your magazine. That will determine your maximum OAL - where the bullet will hit the lands is irrelevant because it won't. Of course we're ignoring pressure changes in your current load, whether the bullet can be seated that far out, etc.
3) If you want to single feed, you can use gauges or other techniques to keep seating a bullet longer until it touches the ogives. MikeinUtah gave you a vid link that can get you started. Of course we're ignoring pressure changes in your current load, whether the bullet can be seated that far out, etc.
Have to honestly say I'm afraid to give any more advice because it sounds like you've heard seating to the lands is a good idea, but don't yet have enough background to understand what factors affect that, how to measure it, and when you should, shouldn't, can, or can't do it. Best I can say is read more, watch more videos, sharpen your question. Sorry if I've misjudged, but better to be safe than.
