Here is my after action report. Using a Rooskie visa to enter Belarus for 3 weeks. As an Amerikanski.
The land crossings at poland and lithuania are brutal. They will process about 1 bus an hour.
The bus from ride from warsaw to brest took 15 hours. And i cant return the same way. The bus ride from Minsk to Vilnius also took 15 hours.
If you enter Belarus first and plan on crossing into russia, BE SURE THEY ISSUE YOU A MIGRATION CARD. Or else you will be illegally entering Russia.
If you have a Migration card you should have no trouble flying from Minsk into Russia.
Due to the 3rd grade antics at the land borders, i would highly recommend entering Russia first and then taking a train into Belarus. I would suggest flying into St Peterburg and taking a train into Belarus.
All the main cities in Belarus are clean and reek of the old USSR. I visited Minsk, Brest, Grodno, Gomiel, Mogilev and Vitbsk.
Some credit cards and ATM cards work in Belarus. I had good luck using PreorBank ATMs. All buses take cash.