For starting trees indoors, I'd recommend rootmaker express trays and cheap shop lights. You can use florescent bulbs or, even better LED. Light energy diminishes with the distance squared. Expensive grow lights are hot and must be kept quite a distance from the trees. The florescent and LED lights are cool and can be hung close. Tress can be reorganized by height with the express trays. You can then hang the shop lights at an angle to keep them a few inches above all trees. You can use chains or prussic knots to adjust the lights. Lumens are important for trees, not color (wavelength). Trees spend such a short portion of their life indoors that they don't go through the growth stages where specific wavelengths are needed. 3-4 four foot shop lights with 2 bulbs each hung a couple inches apart will provide enough light to cover 6 express trays which is a little over 100 seedlings.
Much more space is required after they have been in the 18s for 16 weeks and need to be transplanted to 1 gal RB2s. I try to time this so the transplant occurs about the time our last threat of frost has passed so I can begin the transition to full sun as soon as I transplant.
Best of luck,
Jack