Was there over Christmas. Travelled from North down to Agidir and back up to Marrakech. Very hot everywhere. Essaouria is very lovely; wasn't very touristy then and some great restaurants. meant to be much more popular now, but should be lovely.
Guess so, like anywhere different experience depending upon number of days. They do advertise 'long weekends' in morocco so go for it. We were there 3 weeks but travelling around so you can go for sumptious luxury for 3-4 days in one place I'd def choose Essaouria for that but stay in one of those beautiful old riads with the courtyards rather than modern hotel