Depending on exactly what sort of coverage you need, you could get a number of outdoor wireless access points to cover an area and/or use pairs of directional antennas, connected to access points with removeable antennas/antenna connections, to create wireless links between locations. Some dish antenna setups can carry WiFi signals over a few kilometres.

A few CCTV cameras are unlikely to overload your hub (broadband router?) but there is something to be said for having routers handling routing (i.e. your broadband Internet connectivity) and switches to handle switching (providing cabled Ethernet connectivity). This also means that your cabled connectivity and any wireless access points connected to it don't need to change if you change your ISP and get a new hub/broadband router.