Hi Johny and a big welcome to the Forum. It's always a treat when we get another member from somewhere else than the UK, its interesting to find out how people keep their poultry in other climates and different conditions.
Quite a few of your questions might be answered on the Poultrykeeper website, (see link at the bottom of the page) which has lots of good articles on keeping chickens, including feeding, housing, worming, parasite control etc. We do have another member, Chris, who recently moved to southern France (with all his many chickens!) who will be able to discuss local conditions with you, such as the temperature difference winter and summer and how to deal with it.
However, one or two brief pointers in answer to some of your questions. At 8 weeks old in the UK it would be usual to feed them growers pellets, which are formulated for the needs of a growing bird and don't contain so much calcium as layers pellets, which they move on to when they are ready to lay at around 20+ weeks. If growers pellets aren't available where you are then I expect what you are feeding will be fine, though be aware that maize is very fattening and heating, good for the winter but may possibly cause them to put on weight too fast if there is much of it in their diet. They shouldn't have loose motions at all, this will need watching as it may possibly indicate a gut infection, although if they are having too much fruit peelings and other human food this may well be the cause. It's best not to give any human food leftovers - this is actually illegal in the UK, in the wake of the BSE and other disease outbreaks, and for the birds themselves it can be harmful as it unbalances their diets at a stage where proper suitable nutrition will have a lifelong effect as they are growing. Hens are like us, they will pig out on what to them is junk food, i.e. human leftovers high in salt, sugar and fat, and them will leave their proper food because they have filled up on what is not good for them. So maybe you can politely get your friends to eat their own leftovers! If they can free range they will get greens and bugs to supplement their diet, but if kept in a run they will like some greenstuff such as cabbage etc, in quantities which won't upset their bowels.
Chicks are usually vaccinated in stages when they are younger than yours, and this tends to be done more where they are being raised in large batches commercially, rather than by a small breeder. If yours haven't been done, don't worry about it, your vet won't do it and if he did it would be very expensive as the vaccines won't keep once opened and come in batches of sometimes hundreds of doses for large flocks. So long as they are healthy and don't come into contact with other unhealthy birds they should be OK. The vaccinations are mainly for chicken diseases such as Mareks or Infectious Bronchitis or Mycoplasma (you can scare yourself by looking these up if you like) There are no vaccinations against parasites, you just have to keep checking your birds and their housing for signs of redmite, Northern Fowl Mite, fly strike etc. just get informed about what all these will look like if you get them (as you probably will!) and find out how to deal with or prevent them as far as possible. It will be good t worm them with Flubenvet when they are about 18-20 weeks old but they won't need this until then. This is the only effective wormer licensed for poultry off prescription in the UK - again, look on Poultrykeeper for more details about worms and worming. You will ned to treat them with Flubenvet every 4-6 months. Be aware that herbal preparations do not kill worms, they are more of a tonic but not to be relied on to do the job.
And keep on asking questions on here - good luck with your new birds, looking forward to hearing more from you when you have time!