Deepforest, Seville is a wonderful place. Visit this page to find out anything you want to know of Seville: exploreseville.com
Easter is a very busy time in Seville. If you haven't made reservations yet, you better do so as soon as you can. You may even have to stay out of Seville and train/bus into city.
Recommend you take a day or two to see Seville.
The A'burgs will be open.
See thread in the Plata room subject "Via La Plata Late March 2018" for more information.
Many stay at Triana Backpacker A'berg/Hostal.
I, and many others, prefer Hotel Simon. One block from the Cathedral.
Get your pass port at Hotel Simon. First stamp Cathedral. Also get stamped, for memories, at Hotel xxxxx. Where you stay at.
Go to Via Plata room on here for much information about the Plata.
Yes you can fly into Seville.
Yes you can walk the Plata for 10 days out of Seville. But, you may have to bus back to Seville for flight out. Or could catch bus to other parts of Spain.
Weather should be nice. May be little hot in the mid day - late day. Hot; but, bearable. Nothing like July - August in Seville.
Take PLENTY of water.
Compared to the Frances, there will not be lots of walkers on the Plata. So, if you want to meet loads of fellow walkers -- the Plata may not be the route for your walk.
If you walk on Easter Day, many places may be closed. i.e. stores, bars etc.
Did you consider doing the Ingles instead of Plata?