1. AceKard 2i can works on DS Lite.
2. AceKard 2i running AKAIO 1.6 RC2 can run almost anything including Pokemon HG/SS without patches.
3. Yes, you can download save files onto your SD Card and use them for games on your AceKard.
4. The biggest .nds file I've seen to data is 512 mb. Haven't seen any other one that big though. Most DS ROMs are between 64 to 256 MB