Russia's professional army plus reservists was about 2.1M before the war.

Add 2-300K volunteers who signed up since to replace professional soldiers departing, out of patriotism or because pay was increased 3-4x. Even with all that, Russia still won't have drafted anybody in the pool of about 20M ex-conscripts who went through basic military service in their youth.

They can absolutely sustain that and much more from a purely military point of view. Of course, if you involve public opinion in these matters, 1'000 a day is indeed a bit much for what is not a defensive war.