It will be busy, but not like Cornwall on a bank holiday. I’m not really familiar with the Cardigan area, but the area around Newport is nice.
If you could be tempted further south, there are a couple of spots worth stopping at.
1. Abereiddy Beach – https://goo.gl/maps/Dd6X9 you can cheeky camp on the car park here and walk across to the Sloop Inn at Porth Gain. It’s where they do the red bull cliff diving (http://www.redbullcliffdiving.com/en_GB/video/video-red-bull-cliff-diving-pembrokeshire) but is quiet the rest of the year.
2. Porthclais Farm Campsite http://porthclais-farm-campsite.co.uk is going to be the quietest around St Davids – very old school, field and toilet block, but stunning views and direct access to the coast path.
If you get bored, you can learn to surf or go coasteering with these guys – http://www.tyf.com
Have fun