[RogerBW]

Usual disclaimer - I don't speak Mage so I may trample all over setting assumptions.

In 1905 London had finished its explosive growth phase; in 1902 it was about 6.2-6.5 million and topped out at about 7.5 over the next century.

Having a telephone is vanishingly unlikely, though. I haven't been able to find hard numbers, but I think it's about 1-2 telephones per ten people in London, 1 per 10 in the country as a whole. 1905 was the year the National Telephone Company and the Post Office started allowing interoperation (though only between subscribers in the same local area).

I'm not finding any relevant maps at Perry-Castañeda, but the David Rumsey collection at Stanford (davidrumsey.com) has five maps of parts of London in 1901. Somewhere like Fulham is working-class with genteel pockets, and might offer enough space for what you're after. There's some sewerage there, but it's certainly not universal.

If there is electricity, it's locally generated, probably a few streets away at most. Reliability and price vary enormously. So does voltage - every supplier chooses its own! (If you look up catalogues from the period, you'll see that you have to specify your local supply voltage when buying e.g. a wireless set.) It would be quite usual for a house not to have it at all.

The Metropolitan Water Board was created in 1903 and absorbed the private companies that had gone before. I think that if you want mains water you can get it.