If I was asked to carry out the window cleaning on a substantil propertym but had only limited experience / tools / knowledge, I would consider, first of all.
Is this going to lead to ongoing work
Can I do a satisfactory job
Might I be better farming out the job and taking a commision
You don't really "lose touch"in carpet cleaning, through inactivity, but you may lack the most suitable equipment to get the best possible result
You are almost certainly looking at carpet tiles, rather than, fitted carpets, so your machine might not cope with the job.
Otherwise...................base your price on a time, basis, but you will be guessing and there's no point asking for help on that subject, as the times quoted, will vary hugely.
I'm afraid it has to be your own guesstimation