Not familiar with these but leaves look thorny. Does prospect of getting stuck by these for many years excite you? Normally collecting done just before buds open in Spring or after Summer hardening off of growth.
Iffy material. In general, non-deciduous holly species don't work so well for bonsai. They tend not to ramify all that well. This trunk, however, might be worth digging IN THE SPRING, if you haven't killed it by defoliating it. Have no idea about how easy these are to dig. Thorny leaves are an issue also, hope you have workgloves to trim and prune in the future.