Made a custom chapter focusing on a large ground force and strong crafting/tech. Started with 980 marines and 6 land raiders, not sure if that's normal or not.
Found an artifact on a low population feral world. The planetary government handed it over without fuss. I sent the scout company that recovered it back in their spaceship, flying directly to my homebaseplanet...
...where they were met by a huge heretic fleet which included 2 battleships and 30 smaller ships. Apparently no one bothered to tell me that was happening. They instantly wiped out the whole of scouting company, of course. Fortunately the "small CSM force" on my planet doesn't seem to actually be doing anything. It didn't trigger a combat despite having a little under half the chapter defending against them.
At this point I panicked a bit and bargained all our requisition and half our (pitiful reserves of) gene-seed for a crusade license, which I sent after the heretic fleet on my homeworld and that brownish faction that owned the system beneath mine. Turns out that was actually a forge world or something, and absolutely no one came to help deal with the huge fleet.
At least we did well against orcs, killing well over 2000 of them with 10 casualties, only one of which was a death. The heretic fleet is still in my home system, doing nothing. Not sure I want to keep playing at this point though, its kind of annoying how all that detail is put into the ground forces and then the actually difficult part of the game is dealing with space forces.