So I decided to get feldherr cases, to store my x-wing collection in. I am aiming to have 1 of every ship in the game eventually and here is what I have right now:

TIE Fighter, TIE Bomber, TIE Defender, TIE Interceptor, TIE Advanced, TIE Striker, TIE Phantom, TIE Punisher, TIE Special Forces, TIE F/O, Inquisitor TIE, B-wing, Y-wing, X-wing, A-wing, E-wing, K-wing, T-70 X-wing, HWK, Starviper, Proctorate fighter, Kirahiz fighter, M-3A interceptr, and Z-95 Headhunter

I know these cases are a little pricey, so I want to limit how many of these I need to buy. It looks like the bigger ships is where I run into needing multiple case with the precut slots for things like Lambda shuttle, etc. What would be the most effcient way to purchase these cases so that I have something that I can fit every ship in?

I use Feldherr for all my game systems. For storage in the house I use the Storage Box M. Light , cheep cardboard to protect the miniatures and foam on the shelf. These will hold full trays and half trays (side by side) with lots of room on the side to label the contents (I use Avery shipping labels) U started with the Hard Case X Wing Edition but to be honest I have never needed to take that much to a tournament (I have used it when running demos or got other game systems). Day to day transport happens with the Mini , Medium or Maxi . These can hold combinations of the parts as needed for the lists you are flying (Mini and Medium for X-Wing, Maxi for Epic). The Full Compartment Box and Half Compartment Box work very well as they are designed to be the same size as the trays so fit perfect in the cases.

By as much foam as you need it but only pick up the cases that you need when out of the house. Yes the storage box for the shelf.

so After I buy the case I can just buy foam inserts? Like if I get a case that has foam for Decimator, Lambda shuttle and Slave 1, I can later just buy foam with precut for Millenium Falcon, YT-2400, Ghost, etc?

Yes. each foam tray and each case can be purchased by itself but there are many deals in which you buy a set of trays with or without a case and get a discount. Got me it started with the X-Wing Edition Hard Case which comes in three versions Starter, Empire, and Rebel. In the listings you see the ~9 trays that come with them. Once I had a few trays in hand and could better visualize the sizes with ships in them. I started to fill out the rest additional foam orders. Every case is sized for the half foam to full foam and two half foam will always sit side by side in the same space as a full foam so there is great modularity. If any thing slows you down it is hight.

Take your time and study their website to get what you need. As you said they're expensive but, for me, worth the cost in the long term.

It looks like the prices are in Euros. Will the site auto convert my credit card to euros for the order and show me what the price is in $?

if you are in the US you can get them through Amazon.

At the top pf the page is a currency selector. I have always purchased directly and shopping has been very reasonable and VERY fast.