- Visas / passports / paperwork
Passport needed, generally USA citizen don't need visa for such countries you mentioned or any other paperwork than few things they may give while entering country.
- Customs (merch)
Never been a problem. In some countries it is illegal to show certain "symbols of hate", so overtly offensive merch to be either avoided or shipped in advance.
Don't expect things to fly out of your merch table. Depending on situation, sales may be ok, or may be nonexistent. Strong value of Euro currency may be benefit and help sell merch.
- Rail travel
There are things such as Eurail pass. Google for price options. This needs to be purchased 6 months before you come from USA and validated in first day of europe. It can't be bought from europe. That's too late then.
- Typical turnout / support of euro fans
Depends totally on country, day, warm up's, venue etc. It must be just about same as in US. From 10 people to even 100+. Most organizers can't offer guarantees for bands with no local fanbase. So unless you're Prurient or Merzbow, forget about demands, and treat the tour as holiday. It's your own risk, where you may get free meals, free place to stay, and sometimes even some $$.
It really depends on "local scenes". In some places you may have stronger interest for PE/Industrial/ambient, while in other places it may appear to be so, yet there exists no people to go to shows of this type.
- Language barrier a problem?
No problem.
- Electrical issues
Try to get things that work on batteries or if not, get the box that changes voltage. Generally voltage & plugs are the same around europe, so one box will do it. We have more power here, so possibility to burn your gear exists if you don't take care of issue.
- currency
Not a problem. Credit card rule the game now. You can take cash from any ATM anytime. Euro works for majority of countries.
- Do's and donts
Don't expect success or getting your own back. Good time at the best. When nobody does it for money, pretty much every organizer does a sacrifice of time and money to help out. It's not good to make too many demands.
It might be best to focus on trying to get couple "major events", and set up rest of the things on the way and skip the places where is no point. I'm assuming doing all - south europe, north europe, baltic, etc.. it may not be that good idea. Travel takes so much time and money, so it will be probably cheaper and easier to do 2 tours separately, than do everything at once. Especially if you'd do railway, it would take ages to go from Italy to Finland for example. Planes may get expensive. If you book well in advance, you might get good budget prices for flights, yet often these cheapo flights are done to small airports, where you pay great deal of money to take bus to actual city.
