Hey T., I've worked for two different pediatric dentists for many years. You have already received a bunch of good advice, but I wanted to add a couple of things.
1- I would stay away from a "gentle" or oral sedative unless your son sat still and did very well for his exam/cleaning. The reason is that oral sedation calms some kids and makes others ten times more hyper/hard to control. It isn't a strong sedative, so they can easily fight it if they want. If they are already apprehensive, they often (not always) do. That can make for a very bad experience and often you end up having to go with the full sedation anyway. Full sedation isn't bad, I promise! I have seen so many mothers go through it and it is SO TOUGH, but the kids do great and don't end up with a terrible fear of dentists.
2-I would NEVER strap a kid to a papoose board. I have only seen this done 2-3 times, but it was TERRIBLE. I have also treated many kids who had it done in other offices, and they were deathly afraid the the dentist, some even at 14 & 15 years old.
3-As far as the baby root canal...it sounds so terrible, doesn't it? It really isn't! It is actually not very similar to an adult root canal. You don't clean out every canal. You simply clean out the top part of the nerve and put a little medicine in there. I actually think it is often easier than a filling. I know some people recommended pulling it. Space maintainers can be great, but personally I think your son is probably too young. (ask your dentist for sure b/c each child's teeth are different). If you put it in too early (like 2-3 years before the permanents come in) you run the risk of it not working and then have some serious orthodontic problems later.
4-As far a the cap/crown goes....there are two types. The first is metal with a white front. The second is all white. The metal is a TON stronger and will last a LOT longer especially if your kid is a grinder. However, sometimes the white front chips a little. These crowns will also look a lot thicker/bigger. On the other hand, most kids eventually grind through the all white cap in 6-18 mo and have to have it replaced, but it looks a TON better cosmetically.
Hope this helps and good luck! I know it can be so tough. Oh, one more thing...studies show that kids who see the dentist (just for a quick lap exam, no xrays etc) before they are two have fewer cavities and less apprehension later in life, so maybe you could make a quick appt for your daughter. Most good pediatric dentists will do it for free at that age! Good luck!