Very recently I have come back to Delphi after a long pause and written a rather straightforward utility app my client requested to support an older release...
I kno
You say you're coming back to Delphi. If you still have an old version available, use that - every new version adds extra features and if you don't need them them your exes will be smaller without them.
Make sure you're only including units you actually use.
But whatever you do I very much doubt you'll get down to 300k. If memory serves, even a 'hello world' application in Delphi 2 would be larger than that.