Actually Service Level Agreement sets the expectation between service providers and the consumers. It is a type of an agreement insuring how a service provider sets and maintain commitment of his service to the consumer.
The most benefit by SLA is that you'll have a long lasting relationship with your customers, and you can be able to set different pricing for different service level.
Regarding TOS, I'll suggest to get it done by your lawyer, as the law is constantly changing and varies by jurisdiction, remember TOS is not only designed to protect yourself as the host, but also to protect the customer.
If it's well written in terms of legal point of view you might not face any problem for a legal proceeding in future if any dispute arise.