In general, you should be able to collect seeds eactly the same way, except usually at a slightly higher elevation. :) Some genera even have species that vary from annuals, perennials, shrubs, to trees. (Cornus, or dogwood, is a very good example, varying from the barely 4-inch tall groundcover, bunchberry - C. canadensis, to tall shrubs, to those big, graceful dogwood trees.) When they flower and set seed varies, depending on species. Some you can start indoors now, some need a cold period or two (which you can start indoors too, if you like), but since they are large plants, I don't think getting a head start would make much of a difference in size for most species - but it never hurts, of course. A few species do require a regular warm-cold-warm variations, so starting too early may not be such a good idea (maybe in December or January might be a better idea). Good luck!