How many eggs do you hatch per day?

I only use the free incubator. Try to hatch one 5k per day or two 2k. I give priority to the 5k eggs because I don't like them, do try to get rid of them in my bag and keep only 10k or 2k. The reason are events. During an event with more stardust or special hatches it's always easier to clear your inventory of 2k eggs (quicker). 10k eggs are always good and very rare.

After the equinox event I'm taking it easy. I don't even hatch one 5k a day. Need some rest. Also kept lots of special 2k eggs to try and hatch them the next time we get a double candy event (hopefully by Halloween)

Unless the egg contents change to include something new, or there is greater incentive to hatch them (e.g. increased stardust), I normally just use the free incubator, prioritizing 2Ks. If I happen to get a 10K, that will go on a paid incubator immediately.

How many I hatch per day depends on how much time I have to play. I don't have specific goals in this regard.

Latest strategy:
Permanent for 2k
Regular for 5k
Premier for 10.

Provided that it's not raining cats and dogs outside, I may hatch anywhere from 2 to 4 2km eggs, one or 2 5kms, and I use the bought incubator (using money from gyms) to hatch 10km ones if I have any. Sometimes I'm lucky enough to get 10km twice in a row, so I use 2 blue incubators at the same time and may hatch two 10km every 1 or 2 days if I have them.

I use the infinite incubator and walk
(1-2.5km?) worth of distance/day

I run 5-7km in the morning and walk in the evening so typically I hatch ~3 eggs per day. Infinite incubator is always filled with a 2k/5k

I rarely purchase incubators because my RNG is garbage and I find raid passes to be more useful.

Continuing to bank gold and 10k eggs for special events; hoping they increase & discount Pokemon Storage Upgrades when Gen3 is released.

During the event, I was hatching 10-12 a day for the simple fact that, for some fortuitous reason, my GPS drift at home was crazy (it has since stabilized with the last upgrade) and I would clear out my egg inventory overnight with the infinite incubator and only one other purchased incubator.

Now I just use the infinite on 2 km if I get them, and usually have one normal incubator going to churn out 5 km ones, which often lasts for the 3 days required to purchase the next one. I bought 3 super incubators which I am saving for any 10 km (or the Halloween event, whichever comes first).

I don't know, that last two 10K eggs I hatched were a Sudowoodo and a Militank - not real inspiring hatches to get me to keep buying incubators!
(Hatches a Swinub, Spinerak & Natu also this week...ugh,...).