Start up costs..as much as you want but realistically £100 buys a nice house/ run off eBay for around 4 birds. Basic starter birds that are good layers and readily available from a hybrid strain at point of lay like Warrens are typically about £10 each. Food bin, feeder, drinker, food and litter allow another £30.
I have 18 chickens now, it's addictive. I don't vaccinate, the advice I've had is it's not necessary for small flocks. That being said some of my birds are from vaccinated stock.
I use a cat litter scoop to keep the nests clean daily and do a bit of a clean once a week with fresh nest material and turn out all the litter fortnightly. If its been really wet I throw in a bit of extra dry litter over the other stuff during the week. I use wood shavings, but people use all sorts.
I let my birds free range so let them out in the morning and shut them away at night. If you buy a cage with integral secure run you can avoid this. I'd recommend getting a run because it makes them easier for others to pop in on just once a day if you go away. Other visits would be for eggs.
I dispatch my old girls, except for one who we estimate is over five as she's become a pet. You can list them for a low sale price or free on sites like preloved and usually they get snapped up quite quickly.
I've thirteen birds who should be laying. Two are currently broody (sitting on anything that resembles an egg hoping it will hatch), four are ancient laying fewer eggs and will be moving on soon and so I'm getting 8ish eggs a day. I've five chicks i'm bringing on to replace the four ancient girls.
Ages they live to appear to vary. Commercially they get rid of them at about two years old but I usually keep them till around four with some eggs.
My sons and now my daughter (1)have loved having the birds and have all collected eggs from when they could toddle, not without the odd breakage.
The demand for chickens at present is such that if you don't get on with it you probably wouldn't make much of a loss on your costs.