that is correct. Or get the sim at thr airport, they have tons of SIM booths after the baggage carousels. AIS has the best coverage. True is the fastest in cities.
the 1 year ones need to be extended every 3 months. Unless it has changed in the past 2 years, that is how it was for all ED visas when I studied Thai.
Either way, it's not relevant to this post as the OP is talking about a Non-O visa.