1) Smart is conventional account, Smart-i is under Islamic Banking (Shariah compliant) with Commodity Murabahah (cost plus profit) concept. Functionally both are identical (to make sure Islamic and conventional are competitive). However if your source of funds/income for your account is "non halal" (example: business is selling alcohol or pork), then they will most likely decline you from opening Smart-i, and will direct you to open Smart conventional instead.

2) No minimum amount.

3) You can negotiate with bank to opt out during account creation. Since you have existing relationship you don't necessarily need another card.