In reply to the driving and firing bit I've just 'retired' from the Mid Hants after thirty plus years of volunteering in the loco department where I started as a third man (now called cleaner), then fireman followed by nearly twenty years driving. I also spent nearly four years on the main line with Hosking's engines as support crew.
The upsides...living the dream I suppose (although it turned into a nightmare a few times), being on the footplate of and then driving the biggest locomotives in preservation up one of the bigger hills on a preserved railway, managing your crew (their problems are your problems), training and seeing them develop into railwaymen (it has to be remembered that we use proper trains which can bite the same as other trains, we don't play at railways). Also just getting the job right brings a satisfaction in itself, to have a safe day and know that people have gained enjoyment from your efforts.
The downsides....anything to do with steam engines is heavy, dirty, usually wet and carried out in Dickensian conditions. You have to learn to do as you are told on the footplate, realise that it isn't a democracy and the driver is in charge (some people don't get that bit) In any loco department you have to have or develop a thick skin, the 'banter' can be merciless. You have to take responsibility for your actions (some see that as a downside) and be accountable for mistakes especially when in a safety critical role.
When on footplate duties the hours can be long and arduous, on the MHR we have to prep the locos, do the day's work and then put the things to bed. This usually takes us up to the twelve hours maximum allowed. Conditions on the footplate can be trying too, sod's law says that on the hottest summer's day you get a closed cab loco ( for instance on a Bulleid Pacific, especially an original, temperature can get up to 110 deg in the cab especially when working hard up the hill, and as you are not going fast it doesn't really help to stick your head out the side window)
Conversely, when it's snow or heavy rain you are bound to get an open back cab loco, and of course the storm sheet will be missing or ripped. I remember years ago coming into Ropley tender first on an S15 in a snowstorm and the backhead was covered in the stuff...seems hard to believe but true.
So...as I said I've given it up now. As I also said I've had the pleasure of aiming a lot of the best locos in preservation up and down the line, I reckon about 40000 miles worth over the years but I am 70 soon and the prospect of getting up at 04-30 to then go and crawl under a steam loco in a perhaps flooded pit is less than attractive these days
BUT...would I do it all again?