Hi Chuckhead and welcome to the Forum - and to the wonderful world of chicken keeping.
I'm one of the many keepers with a small mixed flock of back garden chickens - I currently have two 18 -week-old point of - lay hybrid pullets, a Columbian Blacktail and a Leghorn hybrid. They will lay a brown egg and a white egg, in maybe a months time. I also have two purebreds - a Buff Sussex (se my avatar pic) who lays pale cream eggs, and Cream Legbar, who lays blue eggs. So I can always tell who has laid that day. So yes, you can keep a mixed flock, but there may be issues about mixing them in the first place, as chickens find moving home very stressful and may fight or even become ill if this isn't done correctly. You are less likely to have these problems initially if you can get your first set of birds all from the same place and introduce them all together at the same time, so the territory is new to all of them. There will still be a few squabbles as they establish the pecking order, but you could put them all in together. If and when you introduce birds from a different source to an established flock, things can be more complicated and it's good to separate then for at least a couple of weeks, partly to let them settle down, but also for quarantine reasons.
Your problem will be sourcing your first birds, if you want a mixed flock from a start.
It's quite easy to find hybrids, which are bred commercially in large numbers, and some are sold on to retailers who offer a good selection of breeds, all kept together, from which you can choose a variety to give different coloured eggs and be easily distinguishable as individuals. They will also be much less expensive than good purebred stock - probably about half the price. They will lay well, be easily tamed and friendly, wont go broody, and very hardy through the coming winter. They probably won't live as long as purebreds and will tend to use up their egg supplies in the first 2-3 years, as they are bred to do this for commercial reasons. Im sure people on here can help you find a good source for these. But the purebreds are not so likely to come from the same place at the same time, as they are often bred by people who specialise in one or a few breeds, rather than the whole range. Also they have often sold out of point of lay pullets at this time of year as they tend to be hatched in Spring and breeders try to reduce their stock over winter. So, if you want to make a start this autumn, you might consider getting maybe 3 point of lay hybrids, which will lay through the winter better than purebreds, and then research sources of purebred stock for next year. This way will also have the advantage of spreading the ages of your flock so they don't all 'retire' at the same time!
For 6 hens you will need at least 12 square metres of run space - and it's best to have a freestanding coop in the run, rather than a small fixed run and coop attached. There are lots of threads on here about coops and runs, and also of course there's the main Poultrykeeper site http://poultrykeeper.com/ (see link at bottom of page) with lots of helpful info on setting up to keep chickens.
Do keep posting with more queries, there are lots of experienced people on here who, like me, have made all the mistakes and learned from them the hard way!
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