Cleaning the espresso machine

I have an espresso coffee machine that I got (myself) for Christmas. Although I love the machine, it doesn't get much use. Probably 10 drinks per week, about half with milk. Most of this use comes on the weekend.
At this level of use, what is a reasonable cleaning routine? I have read that most machines should be backflushed with an espresso machine cleaner about monthly. Is this overkill, given my usage?

I always clean the PF and wipe down the head (and steam wand if used) immediately. I keep the drainage tray empty to keep anything from starting to grow, etc.

Stated another way, should my cleaning routine be based on the number of coffees brewed or time interval since the last cleaning?

Thanks