The only problem you will have is the CORS restriction - so means your server should have the same main domain as yourExperience service
One additional point you mentioned excel - so the normal way is using some csv - I think this will be also better to be solved in Thingworx using the CSVParser extension. Otherwise you need to use some script to convert the json to csv. Also it could be possible that you can use same Excel macros to read the json file - I used in the past such macros but I have no Idea if this is provided by the default Excel installation.
Re: Collecting data from the user and writing to an excel file
This seems like a reasonable solution. I am not able to test nor implement at the moment, as I currently do not have authorization to access to my company's backend database. Will provide an update if/when I do get access.