No one can't promise the 3300 will make your system future proof, obviously we don't know what the next surround processing update will be. From that stand point all of the AVRs we've been talking about are the same.
But, say 4 yrs from now, your income status changes and you get a larger space. Maybe you're in the same space but want larger LCR speakers that might require more power...the pre outs on the 3300 allow you add a 3, 5, or 7 channel amp to give you that extra power without having to buy a new AVR. Even if you keep the same speakers an auxiliary amp will take that load off the AVR. It will run cooler and perhaps extend the shelf life as a result.
Speakers...I wouldn't be overly concerned about getting a specific center channel...3 good book shelf speakers will work just as good. There are a lot of good options you can get 3 speakers for $500US. I have a pair of RBH RB5i...nice book shelf speaker, $120 or so each US.
If you don't mind custom. these will be even better at around the same price from a well respected company.
http://philharmonicaudio.com/aa.html
I keep forgetting you're not stateside, but I'm sure there are options available to you.
In short, yes, that's a good route, a far better than the track you were on initially with the sound bar.