1- The language is one:
Portuguese language is only one, just accent changes. Some regional words and idiomatic expressions are different too, but the language is the same, so don't worry about that.
The little difference between Brazilian portuguese and Iberian portuguese is similar to the diference between American english and British english.
2- Very useful:
Portuguese is the 5th native language more spoken in the world.
It's the 3th more spoken in western world.
The most spoken in South America.
The 6th more useful in internet.
Portuguese is spoken in all continents of Earth.
3- How you will choose one accent?
The best way to choose the accent you like the most is listen to songs.
From Portugal, I recommend singers like: Amália Rodriguez, Dulce Pontes, Cristina Branco, José Afonso, Roberto Leal... and bands like: Madredeus, Rádio Macau...
From Brazil, I recommend singers like: Marisa Monte, Maria Rita, Elis Regina, Raul Seixas, Zeca Pagodinho, Chico Buarque, João Gilberto... and bands like: Legião Urbana, 14 Bis, Paralamas do Sucesso, Capital Inicial, Titãs, Olodum...
Obs: since you're studying portuguese you have to listen to songs in portuguese. It will help you a lot. I speak 5 languages, so I have some experience in language studies. Trust me.
Since now, listen to songs in portuguese all day long.
4- How to beging your studies?
*Go to the site: verbix.com ...and study the main verbs (ser, estar, ir, ter, fazer, comer, beber). Study just the main times: (Presente, Futuro, Pretérito, Imperfeito, Particípio, Gerúndio, Infinitivo) of each verb.
*Try to get Dr. Pimsleur curse. It's the best.
*In youtube.com there are several classes. Search for "learn portuguese".
5- At least, you're good enough, how to develop it more and more...
When your portuguese is good enough, try to read good literature, writers like: Fernando Pessoa, Machado de Assis, José Saramago, Carlos Drumond de Andrade, João Cabral de Melo Neto, Manuel Bandeira, and at least Camões.
I'm Brazilian and professor of portuguese.