Adi

You can use P1.7 by simply changing all UCAxxx configurations to UCBxxx, see here or here

In my code, I don't use assembly, C only. I use bit banging or hardware SPI module.
WS2811 requires very precise timing and using interrupts is not an option (11 clock cycles just to get in and out of the interrupt.)
Your MCU has to run @16MHz to meet WS2811's timing requirements, especially WS2812's, which is hardwired for 800kHz clock.

You cannot, 1MHz is too slow for WS2811.