hello bugman and welcome to masa
great to hear that you want to start out with marines and even better to hear that you are researching and planning before buying, that will save you allot of cash, heartache and trouble. the best thing you can do is plan
i understand what you say when you say that you want to do the small things right and then move onto a bigger tank when you feel you can handle a small tank. But in my experience i have found bigger tanks ALOT easier to keep than smaller tanks. I have a number of tanks but for simple illustration the 30l nano i have requires almost double the input and effort than my 1000l system. The increased water volume, better equipment and more forgiving nature of a bigger system relay does make it easier to work with, and you have a greater array of live stock that will fit into a bigger system, making it a little more fun to start with. IMHO that is.
to answer your two questions quickly (you will need to read up on corals alot more than this) you get a massive difference in corals, and thus a massive array on possible food sources. Some like meaty foods, some like plankton, some like simple filtration BUT they all (almost) like light. Some need more light and some like heavy flow. What I am saying is that you need to decide what kind of corals you like and which will fit into your tank and plan accordingly. But if you go with a small volume tank, then feeding too much (both for fish and corals) will be problematic so you need to keep this in mind when selecting a type of coral you want to keep.
But there are a number of commercially available coral foods you can use to supplement with, although 90% of the food a coral needs comes from a symbiotic relationship with zooaxthela algaes which use the light available to photosynthesizes simple sugars which feed the corals. Hence light being so important.
as to hermits being reef safe.....yes most are. But there are a number of different hermits and some get BIg and can be a real hassle in a tank. Its best to get the dwarf variety, blue or red legged for example.