“SES”?
Socio-economic status. It’s a standard abbreviation in economics and the social sciences. And to some extend in political science too. Sorry to spring that on you unexplained.
It’s the polite way to say rich vs poor, black vs brown vs white, unemployed class vs working class vs professional / executive class vs investor class vs retired. etc.
And how hard is it to register as a member of a party, and are there any other implications of party membership? If which primary you vote in is the only effect of party membership, then folks will just register for whichever party they want to vote in the primaries for.
Well, yeah. That’s the point. Party affiliation is also for when you want to run for a partisan office.
That’s up to your state so YMMV. The party system would work just like it works now with the only difference (in some states) is that you cannot cross over for the primary because why should Dems be voting for Pub representatives and vice-versa. Unaffiliates do no get a vote in the primary because if you want to choose who runs in a party, you should be a member of that party.