All four of the fish you mentioned (platies, mollies, guppies and swordtails) are livebearers that WILL breed and need to b kept at a ratio of 2 or mroe females per male. I also generaly would not reccomend going for a tank that contains all of them as they are not entirely compatible.
As for cycling - I suspect you are reffering to a cycle with fish. Don't do that. Your fish will either die or have serious health issues for life and will suffer through-out and are likely to die young. Read the links in my signature about new tank syndrome as well as about fishless cycling. It's a lot to go through but I guarantee you won't regret it.
Just a note, there's an 'inch epr gallon guideline' for stocking fish that states that for every inch of ADULT fish, there should be one gallon of water. This means that a fish that gets to 3" needs at least 3 gallons of water to itself. The guideline is rather innacurate as it does not take into acount activity levels or behaviour but it is useful none the less.
Mollies get to about 4", though large females can even get to 6" and balloon mollies, on the other end of the scale, rarely reach 3". Mollies are generaly peaceful but can be nippy towards certain fish (eg gouramies) and can produce huge batches of fry. Try to stick to a single-sex group.
Male guppies get to about 1", females up to 1.5-2". They were once considered hardy. They are now rather fragile and short-lived though the larger, less fancy, ones tend to be quite healthy. An all-male group is probably best (unless you want to breed).
Platies get to around 1.5". These are great fish, hardy and small. Still, they are prolific and a single-sex group is best.
Male swords reach about 2-3" while females can get to almost double that. It's best to avoid mixing them with platies (because they can cross breed) and also best to not put them in with guppies or anything else prone to being nipped because they can get rather boisterous. Males may sometimes get into scraps so it's best to keep 1 per tank.
As you can see, if you want to combine all the above, you won't realy have much room for all that much else. Anyway, concentrate on fishless cycling first of all. While you're at it, look at some of the other fish at your LFS. You'll probably decide you don't want so many livebearers after all.
isn't huge, but may give you a bit of an idea 
