I want to keep up a good running distance each week, but also try and incorporate a few Peloton rides too. Can anyone recommend a calculator/site/article that can give me a steer on what’s a ‘good’ distance to run each week? And ideally one that takes into account circumstances (age, weight etc).
I don't think there are any set criteria for what is a "good" mileage each week. It does, as you say, depend on age/weight/current fitness, etc.
It's very personal... but i'd say if you are able to go out four times a week and run steadily for perhaps 45mins, and can generally do that week-on-week, with no issues, then that is a "good" baseline to achieve. At that point you could then begin to think about longer runs, faster sessions, etc.
But to attribute a number to it is more difficult... four times a week as i describe above would probably get you around 20 miles per week... my own "minimum baseline" mileage which i look to clear every week is 50 miles... there's very successful marathon runners in my club who ran 100+ miles per week... generally the more miles you do, then obviously the better you'll become, but some people aren't suited to high mileage, and cross-training/cycling works for them.
Where calculators/etc can come in handy is giving you a rough idea of the pace you should be running, but again you generally need some kind of timed result as a baseline to work out your paces... i think Mcmillan Running is a very popular one, and will give you the sort of paces you might want to be achieving for long runs, faster sessions, reps, etc. But i don't think it will tell you how many miles you should be doing. And i expect it requires some kind of sign-up.
I'm sure there are others which are very similar.