Up to code kitchen receptacles
As noted by some others in comments: Before you do this work, consider exactly what you need. If this is &quot;inspector said do this&quot;, then you should be fine. If this is &quot;I heard that to pass inspection I will need...&quot;, make sure to consider all of:

2 dedicated kitchen 20A small appliance circuits (not 1 but 2, not 15A but 20A, dedicated to kitchen and certain other areas, not shared with lighting, etc.)
GFCI can be at the receptacles (always works, often easiest) but does not have to be there - it can be at the breaker, or in between. Plus only one GFCI needed per circuit, even if there are many receptacles on the circuit, provided everything is wired properly.
Generally speaking, there should be a receptacle within 2 linear feet of the counter (so if &gt; 4 feet, one every 4 feet). There are some exceptions (around sinks, stove, etc.) but that is the basic rule.

1 - I assume &quot;one THHN wire&quot; really means &quot;one set of THHN wires, including hot/neutral/ground&quot;. Note that ground is not needed if you are using metal conduit, but is needed in other wiring methods such as wiremold.
2 - For kitchen countertop receptacles, the circuit must be 20A according to code. That means 12 AWG wire (which you already specified, so that's good) and 15A or 20A receptacles, as long as you have at least 2 receptacles on the circuit (so that's OK too). Based on your description, you just need to use a 20A breaker instead of a 15A breaker.
3 - Running behind lath &amp; plaster (in conduit or using non-metallic cable if that is permitted in your area) vs. running through wiremold is an aesthetic issue but code is fine with either method. You are correct that floor receptacles can't be used here. It isn't that you can't have floor receptacles in a kitchen, but rather that they don't satisfy the requirement for small appliance circuits, which is presumably what you are trying to resolve here.