Mid-levels will be tough for your budget. And I think is a bit long and hot to walk from there to Exchange Square, though most places there have shuttle buses to Central. Both Kennedy Town and Sheung Wan 5-20 minutes from Central, depending on what time you travel. Someone mentioned that just wait till you get here to look for housing, and I think that's best advice. The agents can take you around and show you all the locations :-)
Yes, I have to deal with US taxes, and is a real pain. You will have to pay both US and HK taxes since the USA is one of the few countries that tax your global income. Hire someone here to take care of it (there are plenty and not that expensive) since you have to do both HK and US taxes and may be hard to find someone to do HK taxes in the US.