Hello there Valentino!
Here in portugal we don't really have conventions, we have smaller events, since anime/cosplay stuff isn't as popular as in other countries.
Unfortunatly, on the period of time you will be in portugal, I don't think there will be any big events =S Those happen mainly from August onward, so you'll probably only be able to attend cosplay meetings, tho the two that happen during those months are the most famous ones and with most cosplayers : ) (if you come to Lisbon, that is.)
In February, we have a holiday called "carnaval", it's kinda like halloween, except the costumes don't have to be scary at all, so we usually celebrate it by gathering A LOT of cosplayers in a place called Parque das Nações, we meet new people, take lots of pictures, sometimes there are cosplay photography contests, and finally we take a picture with all of the cosplayers at the event : ) here's the photo from this year! http://www.animeportugal.net/galeria...l_IMG_2739.JPG
The other cosplay meeting is usually closer to summer time, and it's called FUPO, which are the initials for "Feitos Um Para o Outro" ("Made for each other"). In this one there's a small cosplay contest, mainly for couples (the characters). But we never know if FUPO will happen, we only get that info closer to the date of the meeting itself.
Sorry for my bad english, I couldn't find the right words XD; but I hope this helps! Have a good trip and if you attend any of these meetings, don't be afraid to talk to anyone, we're friendly xD