>How big is the Shinshun/New Year's Kemoket? Is it worth going to or should I just go to the Winter Comiket?
Shinkemo 5 is slated to have 170 spaces. It's by far the smallest of the Kemokets and will likely have a similar kemono circle count compared to the third day of winter Comiket. If your interests are limited to kemono, you might have a better time at Kemoket, but if you have broader interests, Comiket is obviously enormous and will have a wide variety of things spread across the 3 days.
>How big are the other Kemokets? More specifically the Kansai one. Is it easy to get lost in them?
>How many circles attend in each one? Do they share a stand or are single participants usually scattered around the place?
Kankemo 7, as your image states, had 500 spaces. Kemoket 8 is planning to have 700. I'm used to Comiket, so even 700 spaces feels pretty "small" to me. You shouldn't have to worry about getting lost. The booths for the circles are just small tables, usually with one or two people sitting behind them. You can find a lot of example photos online.
>How quickly do participants get out of stock?
This varies wildly depending on their popularity and how many copies they tend to print or reprint. There are circles that sell out within 30~45 minutes of the doors opening, while a majority of the eagar participants still haven't even gotten into the building yet. Others will have stock that doesn't sell out for multiple events.
>Is there any sort of code of conduct that differs from Comiket?
It's more or less the same, but lining up for entry into the event is more strict. People completely fill the first trains to get in line at Comiket at 5 AM, but you will be penalized if you show up too early to a Kemoket. Basically just read everything they have on the website and you'll probably be fine.
>How can you order the catalogue by mail in advance? Do they sale it overseas?
They don't usually sell overseas, or at least you probably won't receive it in time. Overseas participants are expected to buy the catalog at the event, but that unfortunately guarantees that you won't get in the door early.
Edited at 17/10/2018(Wed)09:33:35