I don't think you could have picked a better powder for that particular cartridge with that bullet weight. But first things first, you need to spend the money on at least a couple fo reloading books. Pick one for your general load data, and then one for that will teach you the entire process of reloading. For data, I really like the "One cartridge" books because they have most of the powder and bullet manufacturer's data for that specific cartridge. And then a good book, that will provide good reloading instruction in easy to understand termenology is Speer. Their book has easy refrence termenology translation cross over.
RL19 is a slow burning powder for the 30-06 and is easier to do load developement with than the faster burning powders out there. But somehting to be very aware of when using this and some of the other slow burning powders is where to start, which is what you were asking.
Slow burner's will commonly act poorly, and can even produce excessive pressures if they are reduced below published minimum data. When I do a load developement with these powders I always start around the mid range of the data. However, I realize many bullet and powder manfacturer's will have conflicting data, but as long as you abide by one of the two sources you'll be OK. On that note, Sierra usually has some pretty hot data in my experience.
Another trait of these type powders is pressures and velocities will commonly drop slightly when approaching the higher end of the data, often this is when the charge becomes compressed. This has also been the point in which my velocities and accuracy are most consistent. But all actions are different and will produce variations in both pressures and velocities compared to another action of the same exact model and cartridge, so working up is absolutely necessary, don't just start at the maximum charge. Some where in the middle will be fine.
Use only the type of primer listed in the data. I'm not refering to the brand so muc, but rather magnum or standard. Now brands of primers can effect performance in multiple ways, one of which is pressures.
There is just so much more to cover, which is why it is so important to get yourself a really good instructional manual. And in addition to that, high powered rifle is more involved than loading pistol cartridges. Keeping brass trimmed to spec. is extremely important with bottle neck cartridges, and once again because pressures are greatly influenced by brass length.
