Doing 5 this year as well, started running about 18months ago & did 2 marathons last year (Edinburgh & Liverpool). Training didn't go well for either last year so suffered on both of them! but still enjoyed. Determined to get the training bit right & only looking to 'race' 2 of them this year to go sub 4.
Doing Barca in March, but as a training run for London 5 weeks after. Then Trail Marathon wales in June (going to hurt a lot I think!), Berlin in Sept (back up sub 4 attempt if London doesn't work out) & then Snowdon.
So get your training right, build up slowly and get lots of long slow miles in & you'll be fine. Staying injury free is key. Good luck.