I'll help you get some of the answers yourself.
MR33 data sheet: https://meraki.cisco.com/products/wireless/mr33#tech-specs
MR42 data sheet: https://meraki.cisco.com/products/wireless/mr42#tech-specs
MR74 data sheet: https://meraki.cisco.com/products/wireless/mr74#tech-specs
>I would like to know how much MR33 MR42 MR74 can support the user
This is a long and involved answer that has been asked many times before. Personally for an office environment I like to use a ratio of 25 users per AP. I pretty much never go over 50 users per AP. This answer is the same for pretty much all APs and vendors. It is not Meraki MR specific advice.
If you want to give the users a terrible experience you can load thenm up to the maximum - which is 128 users per AP.
This article talks about approximating the maximum number of users based on your performance expectations. @CameronMoody this article could do with a bit of new lipstick.
https://documentation.meraki.com/MR/WiFi_Basics_and_Best_Practices/Approximating_Maximum_Clients_per...
Personally I would incorporate some of the information from @NolanHerring who has written about this many times.
https://community.meraki.com/t5/Wireless-LAN/Maximum-number-of-clients-can-a-MR55-handle-Decent-perf...
https://wifiburns.wordpress.com/2019/03/28/how-many-clients-can-we-have-per-radio/
http://divdyn.com/wi-fi-throughput/