1) Freshwater and salwater bacterias are completely different. Adding freshwater bacteria to a saltwater tank will not do anything other than add unnesisary organics to your water.
Rock is not live, it never is. "Live" is rock wich is usually composed of dead coral skelotons over time and is inhabited by a large array of bacterias, algaes and invertebrates. These critters usualy play a vital role in keeping great water conditions in many marine and almost all reef tanks.
This rock can be an ammonia source becuase their is usually a die off in these critters during shippping (it's shipped in wet newspapers for cost reasons) and as this stuff decomposes, you get your ammonia.
Yes, 10-20 pounds. It actually isn't very much, considering how much rock people with 100+ gallon systems use. In marine tanks, often live rock and/or live rocks are the only decorations, wich is what I suggest you do becuase it creates a more familiar enviroment for the (usually) wild collected fish. I personally only use about 1 pound per gallon, but probably will do more in the future due to the growth of my corals and the increasing variety of corals I keep.
Please note that it's fine to use certain "dead" rock, such as lace rock, limestone (limestone is actually a dead, dry reef) or (you'll find this at the LFS) base rock. This will save you money and also means less is coming out of the ocean. "Dead" rock will become "live" over a period of months provided that you seed the tank with live rock and/or live sand.
2) Corals: with lighting, additives, test kits, buying the starter colonys (buy small colonys or "frags" to lessen cost) yes it is expensive. For some people who are really into the hobby, it's possible to spend thousands of dollars a year. However, that risk is eliminated in a 10 gallon. For a tank of your size, your looking at maybe an additional $50-100 to go to a reef setup instead of fish only.
Hard to keep: Some corals at this time cannot be kept. While others can. Out of the ones that can be kept, there's some wich will require really intensive care, while others (namely the majority of softys) realy need about the same amount of care as a fish only tank. You need to do your own research on wich you think you are capable of maintianing, also on how to maintain a reef in general.
3) Your looking at one or two small fish at the most (maybe clowns), a clean up crew (snails & hermits) and possibly some shrimp. You can also add almost as much corals to that as you want.
4) Personal preference here - bare bottom will be easier to clean, however sand will provide some more surface area for the bacteria's (although it isn't needed with the live rock) and some more area for the micro inverts. In a tank of your size, it doesn't have enough surface area for a functioning deep snad bed, so you can't reap the benifits of a deep sand bed here.
5) depends on what you keep. For a 10g, with soft corals, I would use two
10 watt 50/50 power compact bulbs in one of those plastic hoods.
6) In larger setups normally a protien skimmer would be used... However here it's really not worth the money considering that it's practical to do weekly water changes. I suggest you read this:
http://www.aquahobby.com/articles/e_small_aquarium_filter.php
It was I while ago when I read that, so I'm not sur eif ti mentions that you should have atleast a 15 x turnover rate per hour, created by powerheads, the filter, etc.
Also, if you don't mind dishing out he cash for a protien skimmer... all the better. Sump isn't nessisary, but if you would like to get one to hide your equipment and add extra water volume and stability... again all the better.
BTW, my member page has some links that you will probably help you research this.
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