Is it okay if I get the letters of recommendation now if I'll be taking admission in some USA university during the spring 2018 semester?

You can keep them ready or ask your referees to keep the LORs ready but it won't be too helpful as LOR format is likely to change with every season. And, the university will send them the LOR format during the period of your application. You can always keep the draft ready and edit it later. At leas