I think the best IDE is the one you are confortable with.
To be honest I do not think autocompletion gives a big boost. I’ve never used while programing on tryton and I do not miss it.
On the other hand I think you should add some pyflakes plugin to your IDE to hightlight the errors and warnings while editing.
Having said that, I always recomend having a look at our Coding Guidelines and try to follow them even if you plan to develop custom modules. Once you are used to it, it’s easier to contribute back to thd project.
I do not think it is doable because “Tryton objects” are constructed at run time depending of the modules activated.
I once suggested that a hook could maybe written to create stub files which may help for completion. But I have doubt about the result.
I use emacs with the module jedi, east modulate uses virtualenvs.
I install trytond on the jedi environment for autocompletion Tryton objects and easy go to definitions.
Emacs has interface with version control system for git, mercurial, fossil and others. Also is magit for git.