[quote=@Sigma]
[@Willy Vereb] 
Alright we've come to a decision. I would agree with [@Crispy Octopus] in that the mobile castles would be too large. [@Hyperdrive] feels the whole "anchoring" thing would defeat the purpose of having Jump Gates for the setting. He also suggest that instead of large mobile castles, why not a large fleet of regular sized ships? 
[/quote]First of what's a "regular sized ship"?
I don't think I mentioned castles but you may have read the sheet I linked before. Said castles range from 250 to 2500m in length.
If you flubbed up and meant my mobile colonies, see my second point.

Second, in order to sustain life the O'Neil cylinder needs to be fairly large in diameter, at least a few kilometers I say so centrifugal force based acceleration doesn't need many revolutions per minute to work. Length is secondary in comparison but of course add weight to the artificial environment. The better question is why can't gates be larger? If the gates are the size of regular vessels or even an Arc then it's a massive pain in the ass to navigate through them. Make them a few dozen kilometers in diameter and this concern no longer applies. It might also eliminate other problems to an extent like gate-camping, although this trouble still remains.

Third, I agree on FTL gates that can be anchored being possibly disruptive for the setting. Although I also feel there's a plothole if they don't exist. Then again, story above worldbuilding, I'd say, so maybe we can just accept it and move on.