"Any recommendations from people that have used the train to travel and the best and most cost efficient way to get between some of the countries would be extremely helpful."
When researching transportation options, keep this quote in mind: "Fast, cheap and good... pick two. If it's fast, and cheap, it won't be good. If it's cheap and good, it won't be fast. If it's fast and good, it won't be cheap."
I don't know the rail systems in all these countries, but the "best and most cost efficient way" to travel in Germany and onwards to Amsterdam is either advanced purchase of 2nd class tickets for the high-speed trains betwen major cities (ICE= Intercity Express), or regional passes for traveling to peripheral smaller cities and towns. For the ICEs, you can purchase tickets up to 90 days before your date of travel. Ticket prices gradually increase thereafter. Yes, you lose flexibility because it locks you into riding a specific train, but cost and flexibility are usually inversely proportional. And the daily cost of a rail pass is often more expensive than the full price of second class tickets (that you can buy immediately before boarding) for all but some of the longer train routes. So, often you're paying an extra premuim for the mere illusion of increased flexibility.
For the regional passes, the prices of these do not change, so you can simply buy them at the train station. Some of the other posters on this website know more about these passes than I do, so I'll let them fill in the details. And even if you don't use the regional passes, tickets on regional trains are much cheaper than the daily cost of the standard railpasses.
Most of us have found that third-party rail passes are just about the most expensive method for traveling around Europe. And because some of the various national rail operators have placed restrictions on their use, some of the flexibility they formerly offered is gone. You'll have to crunch the numbers yourself to decide what offers the best value for you. But make sure you get all of your information from the websites of the rail operators in the individual countries (Deutsche Bahn for Germany, NS for the Netherlands, SNCF for France, etc.), NOT from third-party ticket resellers like RailEurope, Eurail... or even the operator of this website. Anyone else beside the company that actually runs the trains is an unnecessary middle-man. Like all middle-men, they'll try to make their services seem indispensible and will only provide you with selective information.
So, your first question shouldn't be "Which railpass should I buy?", but "Should I buy a railpass? The answer depends on your own personal preferences, but for many of us, we determined long ago that our answer is a definitive "No".