Houses in LIME Odyssey for characters require a guild area to place said houses. Your character will be able to own that house as such. From what I've seen, there's no castle siege system at all, nor any guild castle upgrade system. Guild towns also seem to be persistent with the world, or just have a really huge map with mobs / etc. in them.
Houses can be upgraded and furnished, but you need to find the contract form for building said house (from a player that is a contractor.)
Choosing certain life jobs will transform your house into different things, so please be aware of this.