How to drill to insert rebar into a large rock (5mx5mx5m)
A rotary hammer is the standard tool for a job like this, with a carbide-tipped masonry bit. You can rent a heavy-duty model at your local rental center. They're not difficult to use. Be sure to wear ear, eye, and resipration protection.

As for your question about depth, you haven't provided nearly enough information about your plans for anyone to speculate.