Mono Laser does sound like the way to go then.Probably Max of £3 a month
Somewhere around 40 a month
Yes, but very rarely & not really important
The toner doesn't 'go off' so lasts years. The worst you'll get is a small puff of smoke if you haven't used it for months and dust has gathered. Doesn't affect the print and isn't going to set anything on fire...
It's then a question of features that you want, cost of replacement toner, and buying a known brand product with good reviews.
The Brother DCPL2510 that I've had excellent (second hand) experience of has gone up a touch to about £140 but even under heavy use for a year by my good lady wife it hasn't needed new toner which makes it something like £5/month for the first year and a twin pack of 'compatible' toner is about £25 so probably 40p per month to run after the initial purchase - quite probably less - excluding paper of course but that's probably only another £10/year or so.
Things to look for specifically are if you want / need airprint (so you can print from iPhones or iPads directly) and if you can manage without the 'all in one' scanner/copier feature.
I personally just take photos of docs with my phone on the rare occasions that I need to 'photocopy' anything so have a much cheaper laser printer - but if that's a feature you use regularly then a modest extra in the initial outlay will be worth it.