Filamentosa is basically trunkless. If you want the look of a trunked yucca in your yard you could try Yucca recurvifolia or possibly Yucca rostrata. In your climate they would probably require some protection such as a south facing wall. A raised, gravely bed would also increase your chances of survival. Go to the Plant Delights Nursery web site and look at their yucca offerings.

More than likely it's scale and that's honeydew dripping from it. I use a concentrate from expert gardener that works great .

It depends on what kind of yucca it is. The more tropical species, such as Y. gloriosa can be fairly easy to do that with. The hard-bitten desert species are more difficult--it's rumored that it's impossible with Y. brevifolia. If you want to try, cut off about 1/2 to 2/3 of the green leaves; take a sharp saw and make a fresh, clean cut through the broken end, and immediately dust it with sulfur powder (and/or rooting hormone powder); let it dry for 2-3 days in the shade; then put 2-3 inches of the cut end into moist pumice, or a mixture of sand and perlite, holding up the stem with stakes. Keep the pumice moist, but not soggy, and, hopefully, the leaves will suddenly plump up, and the tip start to grow in a month or two. Wait another couple of months, then repot into a cactus mix or other fast draining potting mix. Good luck, Kevin : )

Most likely multiple plants. Recently I have seen stores are getting various kinds Ficus and most are multiple rooted cuttings in a single pot. I guess they look fuller that way and perhaps more attractive to customers. For a multiple trunk tree the individual trunks will be very close to each other at the soil line.