M3 Lite 10 4gb model numbers?

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In the UK I'm seeing 3gb variants of the M3 Lite 10 on eBay etc but no 4gb versions.

What are the model numbers I should be looking for in either 32gb or 64gb with 4gb ram?

Also, I haven't checked yet but I'm assuming whichever hardware/software version I pick up will be software rootable with at least some custom ROMs? Or do I need to be careful which version I get?