[robski]

The wide angle end of your 18-70 lens (18mm) equates to a 28mm lens on a 35mm film camera. The horizontal FOV ( field of view) is an angle of about 64 degrees.

I would think that 18mm is wide enough for most landscape photography. Unless your including tall buildings close up where the Ultra Wide Angle 10mm lens will be required.

To be honest it is only you who can tell if your lens wide enough. Can you get all of your subject in the frame ? if not you need a wider angle lens or move back further.

The best photography is learnt by trail and error, learn from your mistakes and try not to cram too much theory into your head. Use the theory when you need to understand why something does not work as expected.

As Duncan has said before Gadgets don't make the photograph. They only help. It is down to the eye, skill and experience of the photographer to capture the moment.

Often it is the case of making the best of the kit you have got with you at the time. It is all too easy to get hooked on the must have gadget only to find it idle in your gadget bag for years on end.