Visiting Laos For The First Time ~

I am thinking to visit Laos with my thai girlfriend.I have never been there.I wanna know about the whole procedure from bangkok.Which train/bus to catch?I heard that we will have to cross border from Nongkhai.Are all foreign nationalities are entitled to a visa on arrival for Laos?how much does it cost?And after entering Laos,how to go to vientiane?Which buses/taxis go there and the cost?Which guest houses will u recommend which are clean,good and cheap.How to get around in the city?What about the food there?And the worth visiting places?How about getting back to border?I m sorry If i asked too much.