Qt Creator supports c++ and Java and many platforms including android, ios, linux, mac, & windows. What approach for Couchbase Mobile/ Sync / and Server / would you use to accomplish a single code set with many different platforms in mind. Would the Pure Java Desktop Be best, or something else?
Java isn’t available on iOS (unless you want to dump an entire Java runtime into your app, which is kind of crazy.) I suppose you could build a glue layer to bridge a C++ API onto the Objective-C version of Couchbase Lite.
So I guess we should use 3 … IOS, Android and (java or C) is that correct?
We have three versions of Couchbase Lite: Objective-C, Java and C#. There is no C version.
Maybe RoboVM would be interesting to you, it allows Java-based apps on iOS (and doesn’t embark a full fledged JVM in your app AFAIK). This is still in beta, but a few apps are already on the store (most of them games) 
For example Rock Ninja is “only” shown as weighting 22MB on the App Store.