Certified GKH Gardening Expert
There's no need for pinching, though doing so will not hurt the plant. Yes, they will bloom throughout summer. You can apply a balanced fertilizer every 6-8 weeks or simply use a slow-release fertilizer at the time of planting, along with some compost. This should be sufficient and lessen the need for you to continually do it.
Also, deadheading is often a good idea once the blooms fade, as many varieties will self-seed. If you don't want them popping up in unexpected places, this will help. Otherwise, you can let them be and allow them to surprise you with additional plants.