I won on Belitlli as a researcher and it is a combination of both.
For one, you have to beat any other researchers to the punch. Then you have to weigh stealth versus capping as fast as possible and that largely depends on the available resources. I had enough resources to build many many more SCTs than I needed to win, so I just went for capping all of my colony systems as fast as possible once I got going. The benefit of this is that doing them all at once shortens the window for other players to take notice and to attack. Further, if I lost even 20 of them, I could easily build more (to a point) and then defend them in smaller batches at a time. The downside, is that I couldn't really protect the SCTs and they were easily killed if someone took notice. Though later on I was able to protect them better with 50 battleship fleets, if necessary, at first I had too many SCTs running to cover them all. However, if stealth is even more of a concern, you could send the ships to obscure solar systems that are unlikely to be examined.
That said, at some point the traders will notice what you are doing if the server has enough active players. This is what happened to me with one player who had many trade routes to my colonies. Though we had a trade/peace agreement with 24 hours notice before declaring war, he immediatley took out some of the taps (rightly so). Unfortunately for him, 23 of them had already run for 24 hours before he attacked and so I won. I think if I hadn't been capping the colonies where the resources were held, where all of his trade routes visited, and where the ships had been built, he may not have noticed even that quickly.
Now Belitlli only had half a dozen competing players by this time, but I could imagine it being much tougher on a larger server. The other active players were not watching me closely enough and my immediate neighbors had all been taken out through military action, so they were no longer a threat.