So far I've only tried Merlin and High Men, but I've found my armies are typically too weak to take over any lairs or nodes at the start of a game. Summons don't help because I typically don't have enough magic power to support them.

How long should I expect to wait until my armies are strong enough to kill...anything?

Well, I'd say your first truly good unit would be pikemen, as high men. You can build those with the fighter's guild. Armor piercing and reasonable stats make them quite formidable. Ultimately as high men, your bread and butter unit will be paladins (armor piercing, magic immunity, and other goodness) with magicians serving in occasional support roles. Of course, it will take some serious infrastructure to build those units.

If you're interested in more straight forward, short-term power, give the gnoll race a try. Their early units tend to out fight any other non-myrran races by a wide margin. Massed wolf riders are a speedy, highly effective early game army. Gnolls don't have as much late game potential as some of the other races, but, if you aggressively take advantage of their early game power and don't neglect strong summoning spells and unit buff spells to help out in the later stages, you can do very well with them. They're a lot of fun, and the lack of a complex list of buildings to worry about can make them a refreshing choice when you're still learning the game.

Hobbit Slingers - with an Alchemist's Guild providing magic slings.

Don't listen to this people telling you what to pick, just learn the difference on magic and units, learn the basics of 4x games and play. Obviously you will lose the first few games but if you learned something and apply it later you will get better. Before you know it you will be able to win with any magic and any race.

So, does this mean that lairs and nodes are simply out of reach before I tech up?

For lairs, temples, ruins, pretty much all of those (not including nodes) best thing is explore them to grab the unguarded ones. Once you can form a strong army attack them.

For your question, if your attacking them as soon as you start the game then yes they are too strong because they are free mana free gold and sometimes research for free, obviously the game won't give you those that easily lol this is an old game remember we don't know what easy means lol.

Just make sure to have guarded cities because if you take too long those ruins will send raids at your cities and destroy them to become new ruins to take out.

Don't attack ANYTHING straight away - spend a few - well, a lot - of turns just building up your city, building support structures like Barracks, Armories, Alchemists, etc. Then build some decent units and look for nearby towns (or, if you feel pacifistic, good locations for your Settlers to make new ones).

Only when you have a competent army of a half-dozen or so good troops should you think about ruins & nodes! Especially nodes - you cannot rely on magic there, but magical weapons (via the Alchemists' Guid) work. Leave a couple of troops minimum at every city on garrison.

Summon spirits (what are they called again? Just Magic Spirits?) and bind them to nodes you capture ASAP, they can help a lot later. I'm not sure if you need to guard nodes - I don't remember ever losing one to an opponent.

I don't think anyone is "telling" him what to pick. Options are simply being provided. Personally, I think it's the number of options this game provides that truly makes it great. I agree with the rest of your advice, however.

Sort of.

I think maybe the easiest way to get some good killing power early on is to take all your books in one sort of magic then summon the most powerful creature possible--gorgons are a good example, especially since you can cast 3 decent buffs on them right away, and they can fly.

Flying means that you kill part of an enemy group and often (depending on what you're facing) just press 'done' once you're too weak to kill more, then heal up, go back in, rinse and repeat.

You mentioned not having enough mana to support them, but there's a way around that. Before you cast the summoning spell, put all your magic into mana reserves for a while so that you can afford to spend some turns losing mana. And scout out for a weakly defended node to start earning it back ASAP.

I usualy cast a few spirits to scout the whole map and grab all unprotected lairs and maybe a few low protected cities. All defenders above spearmen are mostly to strong for them.
BTW you can suicide them on nodes to look how well deffended they are. Ok im still not playing on the highest difficulty. Its time consuming but a good way to scout for future settlement locations and gold/manna.

Playing High Men (as I often do), I generally start out focusing on building Farmers Markets, settlers, and swords and spears to garrison new cities, until I've grabbed all available land. Only once I've done that do I send out armies, and their first order of business is generally the nearby neutral cities. Once they've got some experience, I send them against things like zombies, then skeletons, then ghouls and war bears and stuff... and by the time I throw them at something that's more than they can handle, I've got pikemen, priests, and wizards coming on line, with paladins not far behind.