I will have a layover in Bangkok for for the first time but only for about 48hrs. Arriving on a Friday around 10am at BKK and departing on a Sunday around the same time out of DMK. I'd like to try to make the most of it.

Any tips on areas to stay? With so many cheap hotels its a bit overwhelming. From what I've read, staying in the Sukhumvit or Siam Sq area is highly recommended. However, I read that it is also the center for modern business and expats which brings to mind western chain restaurants. I expect most if not all of my meals will be street food. Are there a few main areas to go with a dense concentration of street vendors? Like the food courts in Singapore?

Being my first visit I figure I'll spend my full day seeing the obligatory tourist sites (ie. Grand Palace) and then walk around china town afterwards. I'm not the type to spend a long amount of time seeing tourist attractions, more like, see it, take a photo, move on so unless there are long lines or far apart, I hope to get through them fairly quickly. I figure if I go first thing in the morning, I should be able to avoid some lines perhaps.
I'm not sure the best use of my time on the day I arrive. I figure it will probably take 2hrs just to get through immigration and to my hotel so all I'll have is the afternoon. Maybe go over to Ayutthaya? I appreciate any suggestions?

Perhaps it would be better for me to stay closer to the tourist and chinatown area like in the Sathorn area. But it doesnt seem like there is much there. I was looking at the Eastin since it seems to be half way between.