Following are my answers to your queries:
1-A: You don't have to do any major changes. Your main .c file can be copied directly in ModusToolbox, provided you check for any API/function changes in the application.
2-A: I would strongly recommend you to download and use latest ModusToolbox and BTSDKs as we have done several bug fixes and feature additions in latest software versions. We have released MTB 2.0, 2.2 after MTB1.1, so it is always suggested to go with latest versions.
3-A: Apart from ModusToolbox IDE, you can use CLI, CyBluetool, Chipload to program the module.
4-A: During API searching for modus we directed to Wiced APIs
>> I did not understand your question exactly. When you are using ModusToolbox with Stand alone BT devices, you should be able to get the Bluetooth libraries and function details in BTSDK. There are not much differences in functions and libraries though, still I would suggest to verify once while developing your firmware. Please check latest Wiced BTSDK information here: GitHub - cypresssemiconductorco/wiced_btsdk: BTSDK (headers, libraries, chip and BSP files, peer/host applications, buil…
If you are very new to ModusToolbox, I would suggest you to have look at following links to get familiar with MTB