If I am drawing plans for a log house (not a "cabin" but a residence), how thick do the walls need to be?

Here take you choice on dimension for log walls ! !

What does your proposed jurisdiction’s building code specify as the minimum R-value requirements? Once that is known, then the log thickness to meet that value can be known or calculated.

Saying that you live in “a fairly warm climate” doesn’t really help. Also, if you don’t need information on R-value (you know what that is and what it means), then presumably you also know or can find the R-value for natural wood logs – it’s not at all impressive, lumber being a poor insulator – so it’s not clear what anyone can add to your knowledge here, unless I just don’t understand what it is that you’re actually asking.

Would the log house have windows?

I think @Tropical_Willie has given you all the information necessary, @Yellowdog?

I stay in a log cabin with 12” walls several times a year in the Michigan Upper Peninsula, sometimes when the outside temperature is 0 to 20 F. It’s heated with a wood stove.

According to the Dept of Energy, warm 12” logs have an R value of 18, compared to a R-14 for a “conventional wood stud wall”.

The place is always comfortable. Once it’s warmed up, the logs hold a lot of heat.

The cabin has plenty of windows and a 4-foot crawl space below.

My step-uncle had a log home in central Kentucky. The walls were, I would say, 12” thick, maybe 14.

I loved that house immensely.

I noticed the “not a cabin” comment.

Not sure how where this falls on the residence/cabin spectrum, but for reference here is the place I was describing.