My recommendation: If you have the choice between both LCD models, go for 512gb over 64gb. The only difference is the internal storage (ok the more expensive one has some coating on the display, but this is minor). The 64gb model is really small and you would need to buy micro sd cards anyway. Plus its not the fast SSD, but a slower MMC storage type. The bigger 512gb model has enough space for lot of games and personal files, that you only need micro sd card if that's not enough for you. And its a very fast SSD type of storage as well. The price differences is extremely low in my opinion, go for 512gb model if you can.
Note: Also be aware this is the older LCD model, not the newer and more expensive OLED model. The OLED model has lot of improvements, not only the screen. Just telling this if you read this comment and are new to Steam Deck.