Hi,
Please re-download HikaShop 2.3.3, the issue you got is related to Joomla 3.3.4 and we fixed it end of last week.
For your first problem, I am sorry but the user can just choose one payment method for one order.
I don't know which payment plugin you are using but it's possible that the problem is related to that plugin.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.