A very small palm is the pygmy date palm, Phoenix roebelenii. It does not cluster from the base, but they often sell groups of plants in one pot to give a cluster effect. It has very rough leaf bases that would be great for plants. In common with all date palms, there are spines at the bases of the leaves. You can cut these off without hurting the plant. People who grow date palms for fruit cut the thick spines off all the leaves to prevent serious injury.
I highly recommend any of the Annonas: cherimoya, soursop, custard apple. They are very easy from seed, form small trees rapidly, and have nice rough bark. The cherimoya and custard apple might produce fruit inside your greenhouse. I think the soursop needs to get bigger before it fruits.
Mangos also fruit when they are small, and are good trees to put things onto. The Manila mango is a small fruit with no strings. These come true from seed. Other mangos grow from seed, but don't come true.
You can get a lot of tropical fruit seed from
Fruit Lover's Nursery in Hawaii. Some of it will not keep for any length of time, and has to be planted immediately. They tell you on the site how to grow the seeds. I just went to the site; they are closed until after January 12, so you can't look at the seeds for sale until then.