We sometimes go for a beach holiday in the province of Almeria Spain and we always have a good time. However, we have only previously been in August or September. We are considering going in March or April. Will it be very busy at that time of year or very quiet? Although, such places can be too crowded, they are also less fun if they are too empty.
Easter ("Semana Santa", the Holy Week) is probably the second most important holiday season in Spain. Coastal cities are usually full of national and foreign tourists which enjoy both the cultural traditions at the city and the progressively warmer weather at the beach, but thankfully not as packed or as hot as in summer.
This year Easter will be the last week of March. Obviously, the weather would be a bit more rainy than in summer... but this is Almeria we're talking about. You'll get some really nice and sunny "beach days" unless you're really unlucky.
For the record, here's historical climate data for Almeria. Average max temp is 18 C in March, almost 20 C in April. Average rainfall is 22 mm in March, 24 mm in April.
Honestly, this might be one of the best moments you could choose to go there.