Hi David and welcome to the forum,
Q1, Yes, absolutely. You don't need to reside in the US to sell into the market there, all you need is a supplier that is either located there or that will ship to the US.
Q2. As per question 1, yes. You are only limited by your supplier's shipping options.
Q3. This is just my personal opinion, but I would favour using a well established market place like an Amazon or an eBay to start with. Now of course the negative aspect of that policy is cost effectiveness due to fees and competition. However, you have to weigh that up against the cost and difficulty of marketing your own website.
If you have the budget and the know how to market your own website effectively, then I would recommend that option 10 out of 10 times, but the reality is that, that option isn't a reality for most people.
Q4, That one is all down to research. You have to identify market trends, possible seasonal factors, supplier costs, level of competition and so on. Anyone can suggest a product to try and sell, but you're just shooting in the dark unless you do the groundwork to quantify their suggestion.
I hope that all helps