Buying an old house. What NOT to "modernize?"
Can I tear down all the dividing floors on the main floor? They are not load bearing of any sort, right?


No. At least half are likely load bearing. You will need to bring in an engineer and likely retrofit by installing beams to carry the load. 


  I like the functionality of modern-day plastic framed, double glass windows, but won't they look "blasphemous" on a classic house, especially from the outside?


That's a matter of opinion. If this is a popular architectural style in your region, there are likely plenty of vinyl window options that try to mimic elements of the classic windows (likely to varying levels of success). 


  Will I "waste" the real wood if I install laminate wood on top? I love laminate floors, they're too easy to clean and are cheap to buy and install, but will refinishing the wood floor cost similar?


In terms of future 'value', I think you'd be much better off with finished wood floors. But that's assuming the wood that is currently there of a quality and in a condition to be refinished. You'll want to bring in a floor person to make that call.


  should forget about excavating the concrete floor or raising the house, even in the future and given more money, because that is a serious hassle, correct?


Again, matter of opinion. It all depends. We can't say if it's worth it unless we know how long you plan to stay in the house, where it's located, comparable houses on the market, soil conditions, etc, etc. The biggest problem is that you don't have a detached house...there's no way to raise your side of the house without also raising the other side.