Let me think... I need a professional housekeeper, a messager, a personal physician,a dozen of pretty maids(God forgive me, one of them love me secretly),a bard who can write new song about my feat.
And, I need an elite personal army, a coach who can train them stronger, a blacksimth so I can upgrade weapons and armors for my army. Maybe I will choice one of my companion to become their commander in war time. I need them to defeat mercenary from other country, greedy robbers, and evil dargon.
I wsh to travel around the world to find suitable guys for my stronghold.
Also ,I need a luxury hall, a billiard room, so I can set a wine party for my subjects, and play board game with my companions.
That's all maybe more later~
You have the right idea, but I want to take it further. They need to focus on the light strategic gameplay. The stronghold shouldn't just happen to be there. It needs to be significant as a political/military feature. It might be a border fort protecting against the semi-hostile wilderness, or it could allow you to rule as lord over a small area. If some villain is marching an army to the big city and your stronghold is in the way, he should have to deal with it. Customizing the look of the castle is fine, but I want to get into features that either benefit your party or have some noticeable effect on the area.
If you control a nearby village then you should be able to give them equipment and training for a militia so you don't always have to run in and save them. Then if you make enemies with a nomadic elf tribe or some religious fanatic and they attack the stronghold, that militia should show up and help with the defense.