For sure 20-30 can pretty engaging. The small guys get a few more tanks on the board over time, and for the bigger dogs they're picking up 2 or 3 more hitpoints a round at least. I think for a new person interested in trying out Iron War I'd suggest playing as the Axis. You can get a pretty good feel for how steel dictates purchasing decisions and how fuel informs movement decisions (definitely with fleets) by beating up on the AI first before trying your hand at PvP. All the resource stuff that might not seem like a big deal in the first round becomes way more critical down the line, esp in rounds 3-4. Japan and Italy quickly have to make tough decisions about how to use their steel and about allocating fuel for movment, and if Germany builds any kind of sizeable fleet then fuel is hugely consequential for them as well. When you get into the higher numbers with ships, or carriers with aircraft, often your fleet/air has to park it for a round or even two rounds, if they need to make a big movement across two tiles to attack/defend a key spot.
Part of me is still not entirely sure how I feel about fuel from a gameplay interest standpoint, since it remains a tough thing to track intuitively (in terms of what the opponent can do with a given amount of fuel), and sometimes it comes up more frustrating than exciting (when you realize you don't have enough fuel to move everything you thought you could haha), but its still pretty novel. Different enough from the standard A&A experience, that I think a newb can definitely benefit from seeing how it works vs an AI opponent. Either taking just one power or the whole team. I like Axis for that since their game is more straight forward and their expansion pattern to gain new production lillypads offers a lot of different options. And there's something to be said for the endgame crush where you are painting the whole map with your colors, or getting yourself off (as Hepps might say haha) on total victory vs the AI, into the depths where a human opponent would almost certainly have bowed out and gone to bed already long ago.
For the playing as the Allies, I think the difficulty bonus probably needs to be higher in the 130-150% range to provide a comparable challenge. Mainly because the first round combats are so consequential. Either that or you can probably give the Axis a conservative scripted opener for G1/J1 with a smaller bonus to get at a similar feel.
Either way though, for the AI to do its thing and muddle into a decent attack plan during the mid-game it needs way more fuel to function. I think for the learning curve its more practical on the fly to assume that the opponent can always move or hit you with any units it has on the board, rather than thinking about whether they have enough gas. Having unlimited fuel for the AI just sort of reinforces that basic gameplay caution, that unless you're willing to crunch a lot of numbers and prognosticate constantly about what your opponent can do with their fuel every turn, you're probably better off assuming they can just get there and defend accordingly.
Its pretty rad right now, but I'd still like to see a rework on the unit costs, esp the double digit steel thing to bring aircraft into line. I think at present airpower makes it too easy to ignore steel as a resource. The fact that they are relatively cheap makes them simple to mass, but they are also fuel hogs at movement (you need all slots available in fuel 4 per unit at combat move), and without a steel cost up front to cap them, you might not realize until you're way into the purchasing game that half the fighters you spent all that loot on have to stay on the runway. I think everything in the roster could have a steel cost if you moved over a decimal and broke it up a bit at the low end.