Multitex is a simple terminal emulator with which a Westinghouse 1642 type terminal can be emulated on the PC.
It was quite widely for access to the Gabriel system in close cooperation with Sitatex Synchronous but has by now been superceeded by Liaison. One of the main reasons for this is the need of a persyst card which has been discontinued.

1 - Can Multitex work with all Sitatex versions?

That depends on which version of Multitex and which version of Sitatex? Multitex V1.x will work only with Sitatex V3 SYNC. Multitex V2.x works with Sitatex V4 Sync and Sitatex for Windows Sync. When using the SITATEX V4 Synchronous applications gateway you have to replace the files startucp.bin and startucp.cfg with the ones found in MTX2.

2 - Can I start Multitex so that I go straight into transaction mode?

Yes, in order to do so start the program with MTX/T.