wll having in mind that you are a native english speaker and have only 5 years to learn spanish if you really put your mind into it you will be able to achieve some fluency but not at the business level heck you average spanish speaker has no idea how to speak properly at a business level for that you have to go to college and be prepared
i belive that spanish speakers are able to gain fluency in english faster than english speakers can gain fluency in spanish
i do think in 5 years you should be able to speak and be understood and be able to understand at least 50% of everything, the problem with spanish is that it has many accents i think is one the languages that has the most accents, the spaniard accent is very heavy and they have their own slang and expression that even sometimes for us south americans is hard to understand some things they say
of course being in spain your spnaish is going to get better really fast, the advice that i would give you is that you should try to learn pronunciation first learn it really really well which i think is the most difficult part for native english speaker since spanish and english are so different
dont try imitate the spaniard accent but try to sound more like a mexican with neutral accent, in the hispanic world the best accent is the colombian and mexican being the mexican the most used in american movies
try looking for american movies, most dvds have the movies spoken in spanish and which is mexican spanish spoken in a standard way, is the best accent to learn if you wanna be well understood now dont maek the mistake of buying mexican movies done in mexico and imitating their accent that accent is heavy and sounds bad and thats the way most mexicans speak
in americans movies in spanish, mexicans speak in a more standard way and it sounds good, all southamericans prefer that accent in movies than spaniard accent