First try reading the “New User” section, particularly “Welcome; Read this first!” Link removed
You will find the links to bike rentals and also a link on crossing borders. As for getting a visa at ALL crossings; there are certain designated international crossing points and many Thai only. You can get visas on arrival at the international crossing points.
Also do a search (upper right hand corner) “search” or just read some of the existing posts. We like to help out people on this site but you need to do a little research also.
In short, you cannot take a non-plated bike across the border. Most rentals do not have plates or registrations. You cannot currently cross the friendship bridge from Nong Khai to Vientiane with a Thai registered motorcycle.
You can go to Laos and rent a bike in Vientiane.
All this is covered in existing topics that you should find easily.