[Suicide Junkie]

Under that system-continent, you'd naturally have multiple planets per system, so build rate wouldn't be a problem.
Keeping players from bypassing countries would be...
And you'd have to give some leeway in the continent bonus. Perhaps a ringworld "capital" with a zillion planetary shields, that has to be captured by troops, which only a solidly-held system-continent could pull off easily.

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On a totally different track, that should be more in line with what you have now;

Why don't you move the warppoints in the current mod, so that they go directly from planet to planet?
That way, combat will start the instant you warp, and ships can be given speed 1. No skipping through countries and bypassing the combat.
Defender gets the warppoint defense advantage too.

If you haven't already, you could have the planet facilities build at three times the rate at which they produce. Ships would take the full turn worth of resources.
You're supposed to get one army guy for each 3 territories, right?
The continent bonus could be spread among the planets via resource value %

EG: The austrailian places would be 1/3(base) + 2/4(continent bonus of 2 divvied up over 4 places) = 5/6 of a ship per territory. 2500 income with 3000 build rate/ship cost.