Assuming you don't fall into the upgrading cycle, you've weighed it up more or less correctly.
A new battery is likely to be your biggest single expense.
Life depends on the number of full charge cycles more than age, although that does play a part.
You will be doing about 3,000 miles a year, which will be about 100 full charge cycles.
Makers routinely say a battery will do 500 cycles before it loses significant capacity, so your three-year estimate is on the conservative side.
The mileage will have an impact on normal wear and tear bike bits, but a proper cleaning and maintenance regime will extend their life.
Inappropriate tyres won't last long, but again there's not much expense.
Lots of commuters run Schwalbe Marathon Pluses.
They are about £25 each and seem capable of many thousands of miles.