I don't actually own an african grey, so can't be too specific, but I can try and give some brief, general answers to some of the questions.
What is the best food? I’m reading lots of good things about pellets?
Don't like pellets. They're not a complete diet as advertised, and the levels of certain vitamins is not always what you want. They also use synthetic vitamins, like vitamin A, which builds up in the body if too much is taken up. Better in my opinion to feed natural foods which contain — in the case of VA — beta carotene, which is converted to VA in the body as needed.
Is one food brand better than another?
Yes. Some brands of seed mix, for example, are awful, consisting of mainly sunflowers and then maybe 5 other seeds. Others contain a wide range of different seed varieties in much better proportions.
How much variety should they get? How much fruit and veg?
Variety is key. Try any fruit or veg you like as long as it's safe. There are plenty of websites out there with lists of toxic foods, including this forum I believe(?). If you find a fruit or veg that you're not sure about, or maybe an unusual variety, don't take the risk and just ask here.
I’m reading things about too much calcium being bad for the bird, how do you measure and regulate this?
Tricky to measure exactly how much. Just don't go mad with foods that are rich in it, e.g. eggs, broccoli, beans
Avoidable foods or ingredients?
As I said above, there's lists around the internet which list toxic foods which you should avoid. Avocado is the most frequently named, as well as all the obvious stuff like chocolate, alcohol, sweets etc.
Is keeping the cage near a radiator a bad idea?
Yeah I wouldn't put it right next to one, radiators dry the air out, and it might get uncomfortable being that near a heat source.
What do you put on the floor of the cage? Someone told me newspaper at the bottom and then woodbased cat litter on top?
Newspaper is fine on its own and much easier to clean out. Sometimes you might see bags of this sort of sandy substrate for the bottom of cages but it's completely pointless and is only going to harbor more bacteria.
Does bird poo smell?
No it shouldn't be smelly.
Can we still use things in the home like scented candles or Incense sticks or air freshener?
Nope, birds have very sensitive respiratory systems and have been known to die when kept around scented candles, air fresheners etc. Non-stick pans containing PTFE are also a no-go, so you'd have to switch to non-non-stick pans, or a safe option like greenpan which have no PTFE or PFOA.
What are your thoughts on wing and nail clipping? Does this need to be done? What are the pros and cons?
No wing-clipping doesn't need to be done and in my opinion shouldn't be done. Nail clipping may need to be done occasionally, but if you provide natural branches as perches this often minimises the need for clipping the nails.
Any particular perches you would recommend? Are some more comfortable/beneficial than others?
Natural branches are the best perches. If you can make your own that's great (again there are lists online of which trees are safe to use branches from), or you can buy perches made from branches, such as cajeput, which has a nice soft bark which can be chewed up and scratched, and a harder core.
If I was to take my bird outside, how do I know that it won’t just elope? I mean I want it to have a good fly in open air every now and then but obviously I don’t want to lose it either.
All birds should be either on a harness (one specially made for birds) or in a cage when taken outside, and you should always be there with it obviously, never leave it alone.
Teflon! I’ve heard loads about this, and from what I’m reading it’s all true! Problem is that we do have Teflon pans and a George Foreman grill etc. What would you say is a safe distance away from these nasty pans? I’m envisaging on putting the cage at least 20ft away from the kitchen with a closed door between too, is that enough or should it be avoided at all costs?
I don't think 20' is really enough, best just to not use them in the house I'm afraid.
Does it need regular vet visits for injections/vaccinations etc? Any other regular medicines or vitamins?
Regular vitamins should not be provided, unless for medical reasons. As I said about the pellets, synthetic vitamins are not the same as natural precursors to the vitamins, and you don't want to over do it. The only vitamin I think needs supplementing is vitamin D3, because the only way you can naturally produce it is through exposure to sunlight. Some people can take their birds out in the sunshine every day, but unless you can do that, a vitamin D3 supplement is good once a week. Most people take their birds for a yearly check up at the vet's (avian vet that is).
Will allowing my bird to fly (short distances in the house) benefit him or is it not really that important? Will it be good exercise for him?
Yes, I think it's very important, not only for their physical health, but just for their general well-being too.
Being on your feet for 50+ years is pretty tough, is there any way to give the little fella a break?
You can get flat perches, and he might roll onto his back to play sometimes or whatever, but actually perching doesn't waste energy for them. When they perch, muscles in their legs tense up, causing their feet to lock on to whatever they're perching on. They're made for standing and it's not a problem for them.