SOM refers to the portion of the market that your business COULD actually capture, as you stated: "[the] % [you] can realistically achieve from the SAM." Let's use an analogy to break this down - and pretend you are talking about fishing instead of project management software. TAM refers to all...
Strikingly.com is pretty good. Wix is also good. Squarespace also good.
The answer to your first question is pretty simple. Basically you are talking about doing an exclusive deal on a (hopefully pattented) item, or just slapping another companies logo on an item which would be a custom label or private label. White label usually refers to SaaS. Cases are all aro...