1. Do RuneMate Bot Author's use IntelliJ IDEA to Code?
Yes, it is objectively the best IDE to use. Although I use the eclipse compiler because it is slightly more verbose than the Javac one.
2. Are RuneMate bots programmed in Java?
Java and/or Kotlin
3. What's the RuneMate Develepor Support...
In the long run $3/day is much cheaper than paying for a private bot. Try get a quote from a developer and see if it is more economical to pay for a private one, but telling you in advance it may not be.
If you meant an overlay that looks similar to OsBuddy i believe that is possible, but connecting to osbuddy client is not possible yet as far as I know.
I have playersensed the camera zoom level, meaning that each account will have a level of zoom which is linked to it's "playstyle". If you could pm me the logs generated I can tweak the zoom-level so that it would not end up stuck. Thanks for notifying me of the issue!
I highly recommend using VRM (Visual RM) in order to create the bot, or perhaps finding one of the few bot request threads where bot developers are openly offering to develop bots.
From my understanding and overlay was in the works to be added to the Runemate API but is not of top priority. One could look at the development tools, of which i believe, one of two, are open-source.