first, can anyone tell me how big is CLAM blockchain?
second, I know I can check beforehand what-could-be-my clam address balance by going to khashier explorer
but is there another way claiming clams other than using wallet.dat
maybe something like converting my btc priv key to clam priv key (if that even possibe) then importing it to the CLAM qt client
The blockchain takes up around ~230MB of disk space at the current height of 69600 blocks.
I see what you're getting at with having to import a wallet.dat, and that's essentially what's being done. Your wallet keys are basically converted to clam keys on import, and there's virtually no danger here unless your machine is compromised. The once imported data is not stored anywhere in the CLAM client, but that's not to say you shouldn't use multiple btc/ltc/doge wallets (you should). However, there's no way to tell if you own or owned the coin without full key pairs (unless I'm seriously missing something here).