Is this for any entity in the map, or is there a specific entity that crashes each time?

Can you share the .fcw with us?

These maps are now in the atlas. Thanks @Ricko Hasche for another excellent contribution.

Note that the Adill, Reefs and Uldir was wrongly scaled, they were about twice as large as the corresponding area on the parent map, so I re-scaled them and edited the scale bars.

It depends what you are going for. To create a top-down overview, any city style should suffice, you'll probably be mostly using the house tool to create your own shapes rather than using finished building symbols.

If you're looking to map the interior, dungeon styles will allow you to do that. I think you're probably be best off with a regular dungeon style, the Castles add-on will probably not give you too much for a magic scool, other than perhaps some castle drawing techniques, but in general, you'll probably enjoy a modern bitmap based artwork dungeon style more.

If you are after the perspective views, then Castles may help you a bit, but it is probably better to start out with Perspectives 3 instead. But a perspective view of such a building is going to be a complex task, so not a good starting point for an inexperienced user.

You talk about floorplans here. Did you create that using the floorplan tool from a city map? Did you perhaps pick a floorplan template for a style you don't own?

Try the print Wizard. Right click on the print button or find it in the file menu. It guides you through setting up the print, including multi-page print.