No borders, so yes, they would necessarily overlap physically. In more sparsely populated areas, of course, you'd likely find most people (and thus, their private property) falling under only a handful of different jurisdictions, and so mostly resembling counties/states as we have today.

But jurisdiction in cases between two or more parties who subscribe to different states/clans/legal systems could be determined in any number of ways: - by (most commonly, I'd expect) arrangements and treaties between the most prominent/populous states; - by having largely mutual sets of common law to begin with; - by smaller states having statutes deferring to others' laws except in particular types of cases (a sort of inheritance system, allowing smaller states to mirror the laws of larger states which have existing treaties and case law); - by arbitration through mutually agreed-upon services, or the federal arbitration service; - or even by federal statute, in Constitutional cases, human rights cases, and cases against states/clans themselves.

Yes, inter-state law could in many situations become extremely complex, particularly in metropolitan areas with diverse populations; however, the low barrier to entry for states and the fluidity with which a person could change their affiliation would allow legal systems to evolve at such a rapid pace that overcomplicated, unjust, or murky bodies of law would be weeded out or refined by actually having to compete with the creation of simpler and fairer ones -- a process that politics today seems designed to avoid entirely.