Welcome to the forum Toadmyster. I am glad to see your enthusiasm.
Lantana is certainly able to survive in tropical climates, in many equatorial regions it has become a noxious invasive weed. Some species of lantana, and hybrids with those species in their background are surprisingly cold tolerant, much more so than the books suggest. I believe you when you say it has wintered successfully in your area, Pennsylvania. From the gnarly trunk, I wager it froze to the ground most years, and what sprouted from the parts of the trunk and root crown which were buried deep enough in mulch that they did not freeze below its temperature tolerance. The taller parts of the lantana, exposed to the elements most likely died back every year.
Hemlock is a species that does not thrive in climates warmer than zone 7, it needs some 90 days at temperatures below 40 F to break down the growth inhibiting hormones produced by the late summer growth. With small seedlings you might get lucky, the first year. No reason not to try.
In the long term, for northern species you will need to figure out a storage area that chills below 40 F, and stays above 23 F. It is okay to freeze plants whose native range includes climate zones colder than zone 7. All zone 3, 4, & 5 species tolerate freezing solid over the winter if they had time to harden off and go dormant naturally in the fall. Of course freezing soils expand, there is the potential to break pots. High quality pottery & plastic won't break. Breaking of pottery is one reason many try to winter at or above 32F, but below 40F. Storage at 45 F will not work well with northern trees, such as larch, hemlock or northern pines like Jack Pine. But it will work with sub-tropical pines such as Japanese Black Pine. If the temps are cold, near 32 F, light is not really needed, though there is some small benefit if it can be provided. If you are running at 45F, evergreens will benefit significantly from having light (subdued, say 1800 ft candles) full sun in dormancy often causes damage. How and where to winter my temperate species bonsai was the hardest thing I had to learn in terms of horticulture.
Many subtropical species, such as those native to zones 7 thru 9, may actually get enough hours of chill in the autumn, if you brought them into the house late enough in the season. I suspect your azalea will survive well enough for this reason. I have done this with a Satsuki azalea or two, and it has worked. I did get better growth on the tree when I kept it cold enough to stay dormant all winter, but I think that was in part because my light garden is simply not bright enough. Keeping Satsuki cold and dormant until it is warm enough to set it outside is my current method.
Light garden. When you construct your stand, my recommendation is to plan to build it with 48 inch light fixtures in mind. I recommend either 4 or 8 lamp fixtures and I highly recommend using the T5 high output lamps. 5700K to 6700K should work fine. I personally use 8 lamp T5 fixtures and this allows good growth with the fixture mounted 40 inches above the shelf. If you use only 4 lamps, you will need to keep the fixture within 24 to 30 inches above the shelf to get roughly 1/2 sun or about 2400 foot candles of light. High light requiring plants can be set on inverted pots to get the closer to the lamps. Ficus will do excellent at the longer distance from the lamps. A good reflector really helps, I prefer the Sun Blaze reflector, a nicely focused fixture, reflecting the majority of the light straight down to the plants where we want it. Stop in at your local hydroponics store, they are great places for ideas. If you don't have a hydroponics grow shop near you, pick up a couple issues of "High Times", they always have the latest, most modern technology for under lights gardening. Light bright enough for Ganja, or Tomatoes is pretty much good enough for most trees.
Hope these ideas help and welcome to the forum.
