Mike, first off, just so there's no confusion, 'American Style' is it's own style of pizza and it's very different from 'NY style' pizza. You can have an American NY style hybrid, but it doesn't sound like that's your goal. Based upon this post and your earlier posts, I'm assuming you're looking to either sell NY style or Neapolitan (NP) style pizza.
The decision whether to sell NY or NP pizza has been pondered over many times for countless hours on this forum. I think the most important aspect of this decision is the demographics of your area. I can't speak for Sweden, but here in the U.S., Neapolitan, in order to achieve maximum profits, generally requires either a densely populated area and/or an area with a considerable amount of wealth. It's not necessarily because poorer communities can't afford it, but because poorer consumers can have a hard time justifying the higher price and because wealthier communities tend to have more adventurous palates. If you were in downtown Stockholm and had a location that wasn't close to any other NP places, then it would be a no brainer. But a 'small town' south of Stockholm... Unless it's one of Stockholm's wealthy suburbs, then I'm not sure how profitable NP will be.
Don't get me wrong, you'll make money with well made NP pizza, but I think, for a small town in Sweden, NY style could be more profitable. I've also spent some time researching Swedish pizza, and, from what I can tell, it's very NYish (basically NY with an enormous amount of toppings), so NY style would seem like a small step for customers conditioned for traditional Swedish offerings.
This all being said, you're the guy holding the peel- your passion (or lack thereof) will show itself in the product. If, say, Neapolitan pizza excites you considerably more than NY, then that passion might, to an extent, offset a demographically challenged area. If you're equally excited about both styles, though, based upon your 'small town' location, my recommendation would be to sell NY style.
Your existing oven is another plus in the NY style column, although I've come across quite a few 'professional two level electric pizza ovens' that couldn't produce respectable NY style pizzas/NY style bake times. If you decide on the NY route, we're going to need some information regarding your oven:
Peak temp on dial
Photos (especially of the electrical elements)
While I applaud your desire to learn, and you definitely can never know 'too much,' in your particular instance, going to school for NY style pizza might be counterproductive. First off, Goodfellas makes absolutely horrible pizzas:http://slice.seriouseats.com/archives/2012/08/skip-the-pizza-and-get-the-sandwiches-at-goodfellas-les.html
and while Tony Gemignani (International School of Pizza) could be one of the best guys in the world to learn dough tossing acrobats from, he has gaps on the pizzamaking side. You don't want to learn how to make NY pizza from a Californian
Even if there were a respectable NY style pizza school that was geared to small Mom & Pop (cafe sized) enterprises, they wouldn't be able to gear the instruction towards your specific needs. Sourcing the perfect flour in Sweden is going to be a challenge, as well as getting the most out of your particular oven. If you've never made bread before, then I'd find a local college course on breadmaking. Other than that, though, I think, rather than a school, a consultant is the best path. A good consultant can train you and help you through your specialized issues. They should also be able to do all the training via a webcam, so you won't have to spend money or time on airfare and lodging.
On the Neapolitan side, should you decide to go that route, regarding the organizations you're considering, I think it's important, rather than looking at these entities as a whole, to focus on individual teachers. It's the not the organization that's going to teach you pizzamaking, but the teacher. You want to train under the best individual.
A big part of Neapolitan training is simply doing, making the apprenticeship, imo, one of the most critical aspects of the process. While you probably can find an English speaking teacher in Naples, if you don't speak Italian, an apprentice-ship in Naples might be a bit iffy. If you can speak Italian, and you want to sell NP, then I'd definitely head off to Naples to train. If you don't, though, I'd probably look into training with either Roberto or Giulio Adriani in NY or maybe Matthew (forum member) in Toronto (if he's offering training yet). Roberto's schedule has been really full for quite some time, so he might not be offering training, but I'd still see if he's available any time in the foreseeable future.
But that's all contingent on taking the Neapolitan route. Until I know more about your area, I think NY is your best bet.
And, as Gene (Jet_Deck) said, if you're really motivated, you can learn everything you need to here.