Madrid and Granada end of April: A bunch of questions!

1- Per the website, afternoons are quieter. (I imagine because tour groups and school groups probably prefer the mornings.)
2- There are private luggage storage places all over Madrid. Try searching within google maps, in the area of your AirBnB.
3- Having a car in town would probably be a pretty big hassle. Maybe day-rentals to get out?
4- Granada, generally
5- https://weatherspark.com/y/36650/Average-Weather-in-Granada-Spain-Year-Round
6- Totally subjective.

1. Just in general, group tours seem to favor morning hours. However, if you get to the museum a few minutes before opening time, I think you may have a peaceful interlude before a lot of other folks show up.
   I went to the Prado in 2015, and there were groups of people in front of only two paintings (Velazquez's Las Meninas and Bosch's Tree of Life). It was no problem to wander off and see other rooms, then loop back. I realize there are more people traveling now than in 2015, but I think the Prado won't be as busy as you may be imagining.

2. Unless something has changed very recently, there's a luggage-storage facility right at Atocha Station, near the (interior) garden. If you want to look for a place closer to where you're staying, just Google luggage storage Madrid and see what pops up.

3. There is bus service to the Alpujarras. The line I used went to Pampaneira, Bubion and Capileira, but I don't think that's the only route.

4. The website timeanddate.com has ten years' worth of actual, historical, day-by-day weather data for most places of tourist interest. The Granada data is for daytime hours only but should still be helpful.

Granada weather April 2022
Granada weather April 2012
Granada weather April 2020
Granada weather April 2019
Granada weather April 2018

There's similar information available for Pampaneira; I didn't check other potential hiking destinations.

For Madrid or other locations, use the Search box near the top right of the timeanddate.com screen, then use the pull-down box just above the graph to change the month and year.

The Wikipedia entry for Granada includes some precipitation statistics that are reassuring--it's a relatively dry area. However, snow isn't totally unheard of in April, and I guess it would be a bit more likely up in the mountains. You'll find similar info in the Wikipedia entry for Madrid.

We were just in Madrid and Granada earlier in March. I'll do my best to answer your questions.

1. I think the best option is to book online for a ticket for entry when the Prado first opens and then go to the spots you want to go to first. We did exactly that with the Royal Palace and it allowed us to see most of the Palace before it got crowded. When we were walking out 2 hours or so later, the crowds had really picked up in the areas we had already enjoyed in relative calm.

2. if you are talking about luggage storage in Madrid, we did use Stow your Bags - Atocha (Train Station) - Calle del Gral. Lacy, 4, 28045 Madrid, Spain. It's a self-service luggage storage operation (no people are present - just use your credit card and a machine to reserve lockers) that was very convenient and located immediately next to Atocha train station. I'm not sure where you intend to store your bags, but I think there a lots of options in Madrid.

3. We stayed in Granada itself and did see much of the countryside so I'm not much help here.

4. It seemed to me the place to see Flamenco is in in the Sacromonte area of Granada. The options I saw in Madrid seemed to be huddled around Plaza Mayor and had people outside hocking tickets which did not seem as interesting.

5. We enjoyed lots of sun throughout our week in both Granada and Madrid (a couple brief cloudy spells in Madrid), but we were prepared with rain coats just in case as I understand that's always a possibility (particularly in Madrid).

6. There are so many amazing places to duck into in both cities for a bite or a drink. We did our own unguided sort of food tours (just bouncing around for drinks/bites) but I could certainly see particularly in Madrid how a food tour would be a lot of fun.

The Prado can be seen fully in one long day, so a morning slot as close to opening time as possible is probably your best bet to see it all. It’s a world class art museum, too, with a really good quality-to-quantity ratio.