For the tab functionality, you can use VimCompletesMe, it will try to autocomplete with a keyword when typing, except on special cases, such as when it thinks it’s a file, it will suggest file autocompletion, and when it’s followed by a . or -> (you can customize it) it will use omnifunc to try and find a match, if nothing is found, you can press TAB again to use keyword autocomplete.

It’s pretty nice. Sometimes I still manually trigger omni-completion or file-completion or tag-completion or whatever completion I need, but it works most of the time :) Also since Gary uses ALE, ALE already provides relevant omnifunc so if you have an LSP installed, such as solargraph for Ruby, ALE can pick that up, provide an omnifunc, and then you can trigger that with VimCompletesMe simply by pressing TAB.