I agree about the White Stars, my friend has one, very attractive bird, and she's still laying occasionally at 5 years old. It is not unknown for problems to arise if you mix unvaccinated and vaccinated birds, but these are very rare occurences and should not put you off getting hybrids. Getting new chickens is always a step into the unknown and many and various things may happen, but none of them are inevitable and most of them are unlikely if you buy from a reliable source, quarantine your newbies when you get them, and give your birds sensible care thereafter. If you want a lot of lovely eggs, from friendly and attractive birds, having hybrids as part of your flock is a very good idea. My mixed flock of hybrids and purebreds have never had any problems, and I know this is the same for other much more experienced people than I am. Yes, hybrids may not go on laying for so many years as some purebreds, but during the time they are laying they will give you bigger eggs more frequently than most purebreds.
I expect you are finding that the bantams won't be ready for a while because purebreds are hatched in the spring and so are not POL until they are 6 months or so, ie in August onwards. Hybrids are often hatched in larger batches over the winter and so are ready from February onwards throughout the year. If you get a couple of hybrids now, it will be more difficult to introduce your bantams in a few months' time because the hybrids will by then be fully grown, in lay, and will resent the introduction of young, less mature, smaller birds. It will be possible to integrate them, but the process will need care. In any case, even if you got two different types of birds at the same time from different breeders, you would not be able safely to put them in together straight away, because each group would need to be kept separate from the other for 2-4 weeks to allow for quarantine and the prevention of possible cross-infection. However, integration would then be easier if both lots were about the same age and none of them had started to lay, as younger birds tend to be less dominant than mature ones and the territory would be new to all of them.
Of course, the simplest plan would be to decide which kind of bird you wanted to keep, hybrids or purebreds, and get them all at the same time from the same place, hence no disease transmission problems from mixed sources and the birds would know each other and be less likely to fight. If you started in this way, they would all be in together from the start with no need for quarantine as there would be no other birds in your flock which they might possibly infect. If you wanted a mixed flock, you could choose a variety of hybrids as many suppliers sell a choice of breeds that are all kept in together, which would know each other, and this would reduce squabbles when they formed your flock.
