Should I crimp RJ45 plugs directly onto this solid cable?

For ordinary permanent structured cabling, terminate the solid cable onto IDC hardware and use a patch lead from there. That gives you a fixed link designed to stay put and a flexible lead where equipment gets moved.

There are RJ45 plugs made for particular solid conductors, but do not assume that any modular plug is suitable. If you genuinely need a direct plug termination, use a connector specifically specified for the cable construction and conductor size.