I had to install a 200 Amp panel with a 100 Amp sub feed.
The conventional wisdom, (from those who knew more than the experts) was that I would need a splitter and a 200 Amp switch feeding the 200 Amp panel and another 100 Amp switch feeding the sub panel.
Locally it is almost always done that way.
But why?
Well, try to find a 100 Amp breaker for your panel in a rural area.
I did it the other way;
I looked for a 100 Amp breaker. When I found one I bought the panel that it fitted.
This was a lot cheaper and quicker than the splitter and switches.
By the panel first and you may not find a suitable breaker in stock.
It's a lot easier to find a suitable breaker and then get the appropriate panel.
Single pole versus two pole?
Do you have room for a two pole?
A single pole breaker is nice if you can find one.
However I would use a two pole breaker before I would pay extra for a single pole breaker.
Delivery time may be a factor as well.
Bill
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"Why not the best?"
Jimmy Carter