I'll be honest when I say that the ins and outs of applying under the EU law are beyond me having not ever followed that route.
So for me to provide any more opinions would be poor form on my part.
Please keep this in mind when reading these forums - all anyone can offer here is opinions and if you are basing your future life on those opinions - you should make sure you're 100% comfortable with the rules and regs about what you're doing. If you're not - you should find a competent immigration advisor. Yes - it's expensive - but this is your future wife we're talking about. You don't want to go through years of pain trying to get her here.
However - I can help with the latter portions of your questions:
Will UKBA somehow put a block on her eligibility for marriage if she tells them she is travelling to the UK to visit her boyfriend?
In itself - no - but the problem is that if she gives up her job and income AND has a boyfriend in the Uk - then this is a concern.
What UKBA ... ahem ... sorry - the Home Office (can't keep up with all these rebrands) are looking for is whether a tourist will return home. The evidence for this is strong ties to their home land. E.g. a job, financial responsibilities, property, family etc. The less someone has tying them to their homeland ... the more of a risk they are. You've said she's planning to give up her job - and presumably her home - so what evidence is there she'll leave in 6 months?
Or should she also mention that she is here to improve her English do some sight seeing, visit other friends in the UK and possibly travel to Spain & France to visit family and friends?
She can say that - but if she then magically gets married (to a boyfriend she failed to mention) and you have to, for whatever reason, follow the UK route - if her comments get recorded, you could end up coming under a lot of scrutiny.
Rule number one when dealing with any immigration authority - always always always tell the truth - even if it means having to take a different immigration path than the one you'd like to.
Does she need to provide an address of where she will be staying?
Will she need to provide evidence that she will be staying there?
(a letter from the home owner for example)
Will she need to produce a copy of her bank statement to show her funds?
Yes, Yes and definitely yes.
The way I told my wife to think about it when we went through our fiancee/spouse/ILR/Citizenship process was this: If you assert something to an immigration official - you should provide evidence for it.
So - if she says 'I've got £500 to spend' - she needs to show the cash or the bank statement. If she says "I'm staying with a friend" - she should have a letter from the friend welcoming her - or have the friend meet her at the airport - or have the friend's phone number!
Simple really - but surprising how few people think like that.
M.