I'm still playing DL myself so perhaps my advice might not be the best but my 2 cents is that you probably should play a DL game or two first but move on to DA fairly quickly because those versions are similar enough. However you might want to get accustomed to DA for a bit before moving on to ToA.

The only reason I say that is that there does seem to be a *lot* of new stuff to deal with in ToA mainly because I think the separate tech trees for each of the races might take some time to get used to.

Again perhaps it's best to hear from someone already playing ToA but that's how I see it at least as far as what to play and when.

As far as what and when to buy, it seems you need both DA and ToA and in that case you probably should get the Expansion Bundle which will save you a couple of bucks over getting each expansion separately.

I think that if you have desires to move into DA and TA, you may want to jump right into DA right away. The espionage system (be it good or bad) changed in DA and in TA it's the DA version right now.

You definitely though want to not jump right to TA. That may be too much all at once to learn. Get your sea legs in DA before thinking about complicating things in the way of the tech-tree shake-up.

Well, I started with the Twilight of the Arnor expansion almost immediately. (As in, I played just a couple Dark Avatar games and then got TA.)

I was hooked. I didn't have a very hard time at all. I asked a couple of questions in the forum, followed the tutorial, and I was pretty much good to go. Not a great player by far, but I can consistently finish games on the Challenging difficulty level with maxed CPU AI.

I would suggest going straight to TA just because it enhances the gameplay so much more. Race-specific techs mean that every civilization has a unique feel, and unique strategy of playing, whereas before TA, every race almost seemed to be Xerox copies of each other. Boring. TA also improves the graphics, while actually using less memory. I quickly got bored of DA and quit playing a long time ago, and I wouldn't have come back at all if it wasn't for TA.

Don't worry about finding it too hard. TA has improved tutorials, as well as more subtle in-game aids to guide you through, such as more information on techs in the tech tree. The tech trees aren't THAT different from each other anyway. (Not nearly as much as in, say, Starcraft).