I leave out spaces(use the underscore char) as a principal after having problems. Calibre can do this for you as part of the "Save to" operation, painlesly.
2G cards are under $10 here. The big ones are $$
Try other formats to see what you like

Not all convert well.
Have you tried EPUBreader here
https://www.mobileread.com/forums/forumdisplay.php?f=211. It integrates with Firefox Browser nicely.
(I am a FF user for a long time) IE, only when I must.
I read EPUB, mostly text. 2G is well over the 700 titles I have stored.
Manga, pictures will eat space faster.