Effective Backend for Real Estate Application

I am looking to develop a cross platform mobile app involving real-estate. I have looked at Zillow's API and I think that will be one of the API's I utilize.

https://www.zillow.com/howto/api/APIOverview.htm

My question is if I were to utilize their API as well as those of some other real estate sites, would it make more sense for me to call those APIs directly from the mobile applications, or would it make more sense to have a proxy server, possibly with my own databases compiled from these sites, that the mobile application would call? I have only read the basic overview of the Zillow API, but it looks like it is limited to 1000 calls per day. I understand it is a fairly general questions. If there are any more details that would help to make a better answer, please let me know.

Also, if you know of any other free/cheap real-estate APIs, can you please provide them?

Thanks

Not exactly sure what your metrics are. But generally speaking, it is a bad idea to hook your mobile app directly to third party API for the following reasons:

1. You do not control the API, if the third party changed their API your app won't work, the user would have to upgrade. But if you isolate the mobile app by connecting to your server you have more control and can have much longer life.
2. Caching/rate limits. You can get the data from the third party and store it (if you are allowed) then share the data with all your users
3. Multiple datasources: Usually you get the data from multiple datasources, so aggregating the data on your server then send the enhanced data model to the app is a lot easier than pulling data from different sources and compiling them on the app itself.