First things first,
You are right, a bigger tank is better in a sense of toxic dilution
There are many ways for a fuge (Plenum, DSB, Cryptic, Mangrove etc) see which you are most comfortable with
A sump is an external resevoir of water so that you can do all your stuff there and not in the main display
Skimmer or no skimmer is really depending on your commitment, if you are those who are always rushing for time, a skimmer is good for you
Filtration depends on which type you are talking about but I personally dislike canisters
Lighting again depends on which type of animals you want to keep
You do not necessary need a overflow to connect the sump as you can use the I-box
Some DOs and DON'Ts:
Try to avoid any metallic parts
Do your research on the animal before getting them
Do not buy LS just for appearence (Sea Apple)
Never fully trust anyone
Do learn to admire and enjoy the hobby