First, I have no
experience with ironwood, never cut it and never burned it. I have burned a lot of
wood over a couple decades, tried to keep my home warm with nothing but the
firewood. I did have a gas furnace though that kept it livable through cold spells. I had mostly Maple, Wild Black Cherry, and red and white Oak. These all grew from seed.
Ironwood is a very hard wood, perhaps the hardest. The reason a wood is hard because it grows slow. I'd suggest you find a piece of Ironwood and look at the growth rings. They say that this wood will grow a foot high per year. If you're expecting that in 8 years you'll have firewood; for instance. In 8 years it will be 8 foot tall. We can guess at the diameter of the trunk. I'd guess maybe 2, 3 inches.
If I grew firewood, I'd want a large piece of ground. I'd scatter a LOT of seed. I'd expect to wait maybe twenty years. I'd want the
trees growing close together to make them grow straight and without a lot of branches that'd make it hard to split. As they grew I might thin them out and burn that. In twenty years the trees will be producing seed which I'd count on to keep my wood lot going. In my area after 20 years I'd guess they'd be 4 inches? in diameter.