@icclemunchy I am nosy about who you are now! I suspect we will have crossed paths on Facebook. If so you can probably tell who I am from details I've given in my posts.
Some general points arising from more specific questions already answered:
Breastfeeding: Breastfeeding and babywearing are separate skills. I would suggest mastering both before trying to put them together. Though some people struggling with breastfeeding find it easier when they try it in a sling.
Personally I found it easiest in a buckled carrier (though I have fed in every type of sling, from birth to 22 months, which is when I started back carrying), as I could just loosen the buckles and drop the baby down to feed, then tighten up again afterwards. Though as already stated, it is acting as a carrying aid in that situation, not a sling, so it's not hands-free and you need to be conscious of their airway.
Some people like ring slings to nurse in, though if you have it on one hip (they can go in the middle too) obviously they're probably only going to be able to reach that side.
Cheap, unbranded, or fake slings: Nothing inherently wrong with them. Some potential issues could be unsafe dyes, poor quality stitching or hardware. The ones most commonly faked are Moby wraps and various brands of buckles (e.g. Ergo). There are some ways of identifying fakes, e.g. spelling mistakes on the label, wrong logo for the version it's supposed to be etc.
Appropriate age for carrying: Birth (including premature/low birth weight babies, with appropriate care) to as old as you both want/can manage! I carried my daughter till she was 4.5. From 4 onwards it was only to Wood School once a week, as she didn't want me to leave her there, so I at least wanted the journey to be pleasant for her. She would have preferred to continue being carried (though many children will be insisting on walking long before that) but I had had enough by then; she was just too large/heavy, especially going up steps.
I know some people who carry older disabled children though. And I've seen photos of people carrying adults, just to prove it can be done (though that may void your warranty!).
The Best Sling (TM): Does not exist per se. Disabled people will know their bodies and needs best themselves, and with assistance at a library or consultation should be able to find something that they find comfortable. Ditto with non-disabled service users. Especially with buckled slings, which tend to be more structured than other types and may suit different body types/shapes. Some people may need to build up to carrying for longer periods, especially if they've had back/joint issues, or haven't been carrying from birth so their child is heavier when they start.
That's why it's been reiterated so often on this thread that trying some out is the best way to find what suits you. Sometimes well-meaning babywearers will say "Oh X is the best, get that". But while X might be the best for them, it might not suit someone else. And it can be a very expensive way to find that out. In the worst case, people will end up thinking babywearing is just not for them, when they could have been perfectly happy with a different sling, or help adjusting the one they have.
If trying them out isn't possible for whatever reason, feel free to ask more detailed questions and I will try to assist remotely in various ways.
Here is a map of libraries and consultants in the British Isles: www.tinyurl.com/slingmap