You've posted this under SD-WAN, but your question makes it sounds like you are talking about WiFi. What type of device you do have?
If you are talking about MX devices have a look at this sizing guide.
https://meraki.cisco.com/lib/pdf/meraki_whitepaper_mx_sizing_guide.pdf
If you are talking about MR - and the information is a little vague to really answer - then AutoRF will take care of most of the issue for you.
https://meraki.cisco.com/lib/pdf/meraki_datasheet_auto_RF.pdf
You could also consider getting a professional site survey done by a local company to plan out AP quantity and placement. Ekahau is a stand out product in this area that most professionals use.
https://www.ekahau.com/
I've never personally used it, but if you feel like splashing some cash, they also make a version for IT generalists now. You'll probably get a better result getting an expert in surveys to do this for you though.
https://www.ekahau.com/products/ekahau-connect/survey