At such an early stage, I think an apartment works quite well. My cofounder and I share an apartment (with a couple other friends) and things get done. Integrate your startup with your life because the startup is your life if you're serious. But it really depends on you as a person. If it's just that you're somebody that needs to be supervised/forced in a specific environment to be productive, then you might reevaluate your ambitions in starting a company.
I don't see it as black and white. Everyone has their conditions under which they work at their optimal level.
Identifying those conditions and finding a way to make it work I think is more important than forcing yourself to work under difficult conditions SIMPLY because you are a start-up. There is a huge misconception that just because you are a start-up you HAVE to make your life difficult. It already will be difficult; if you can find ways to make it easier you absolutely should!
I'd agree. The more environments you can work in the better, but often will power is as much about being smart enough to give yourself the ambient conditions you need to succeed as it is about just mandating how you are going to behave.
This only goes so far though. Daniel's probably right that you're in trouble if you require another person to motivate you to do work, but I don't think that's what you meant in the first place.
What I said may have come off more stringent than I had intended. Of course there are optimal places; that's a given. I mentioned an extreme case: absolutely requiring very particular conditions to work, an office for example. I'm saying that startups greatly benefit from adaptability, and if you can hack away in your apartment (integrated with living), it likely will be the most productive stage of your company's growth.