If you want to get into forestry, I would personally recommend (because it's what I do) you get into peat production first.
The peat you grow can then be used in Peat-fired engines to power several forestry farms. I think the wiki says something like one peat farm can power up to 10 peat engines.
I tend to use 2 peat engines for my forestry tree farms (1 for the arboretum, 1 for the logger)
Another tip I could give is that you can use a Turbary (the thing that harvests Peat) to harvest two layers of peat bogs. By two peat bogs I mean your regular layer of peat created by Peat Bog #1, then a 2nd story and a 2nd Peat Bog #2 above that.
Just offset the Turbary one block higher than Peat Bog #1 and it will reach (and harvest) both the peat below, and above (from Peat Bogs #1 and #2 respectively). Using only 3 peat fired engines to power the whole thing (two on the peat bogs 1 and 2, and 1 on the turbary) leaves 17 remaining Peat-fired engines that could potentially be powered.