A good area for night life is around Nong Bua temple/Ubon Square or Klang Awut. There are plenty of hotels fairly near, cheap taxis everywhere. I can recommend Nevada Hotel or Sunnee Grand Hotel. It's a great city. Enjoy!
You apply for an evisa from the RTE London. It gives you 60 days and you can apply for a 30 day extention at your local Immigration office in Thailand.