You will need to learn hw to cycle your tank, preferably a fishless cycle, before you add any fish to your tank- you can learn how to do a fishless cycle in the pinned articles at the top of the beginners section.
As to the livebearers, if you are going for a mixed gender group have at least 2-3females per male, although livebearers can produce alot of fry on a monthly basis even if a male is not present in the tank so you may want to consider just going for an all male group although you will need at least 5males and with the mollys this will stock your tank to its limits.
I do not advise the tiger barbs simply because they are very agressive fish to pretty much every other fish out there and you need a large group for them to work although will not be allowed many in your tank since they are very active fish- we are talking about 8barbs here max which would alos overstock your tank.
The other barbs will not mix well with the danios as they do not fair well with active or nippy fish like danios.