With a dedicated server, you can install any operating system. Cloud VPS offers a limited selection (at Liquid Web, it’s CentOS 6, CentOS 7, Ubuntu 14.04 LTS, Ubuntu 16.04 LTS, Debian 8, Windows Server 2012 R2 Standard, and Windows Server 2016 Standard Edition.) Otherwise, both options give you full root access with control over the OS and all the software in the environment.
The main problem faced by users paying for VPS through bitcoin is the fact that while payments to VPS service providers are generally monthly, bitcoin generally does not support recurring payments. This is mainly due to the fact that bitcoin is a push technology i.e. a transaction which has to be initiated by the publisher rather than the client or the receiver.