Seems good so far!
Looking at other sets using the same title in our dats (Basket Manager) i could find hits on C64 and Amiga:
Basket Manager, The (1990)(Simulmondo)(en-it)[cr F4CG]
Basket Manager, The (1990)(Simulmondo)(en-it)[cr Softwar]
Basket Manager, The (1990)(Simulmondo)(IT)[cr ACC - Defjam - CCS][no cracktro]
Basket Manager, The (1990)(Simulmondo)(IT)[cr PDX]
... knowing nothing about the sets, i guess the game was released for various systems. If that info is indeed correct i guess ", The" could also be missing from the title (if it appears on the atari st sets) and maybe the Italy country flag too. Obviously, other sets information should not be taken as correct because many times it is not (as you just discovered

). C64 sets have lots of mistakes and Duncan is currently taking care of it (although it is an huge job).
About the procedures, to create wip dats you use any method you find better. If you are careful enough you can make the changes in the dats with some text editor and save it with updated headers and name.
On the other hand i guess most of the renamers prefer to have the sets and rename the zipfiles (and in many sets the romfile inside the zipfile), when you feel you did a good amount of work, just create a datfile using dir2dat function of clrmame for example and upload it.
Your dats will be later checked by someone and included in the current wip ones, waiting to be released some day

There are other details or hints that other renamers might give you, that's all from me since i don't rename.
As a final note, if you like you can help in other ways too. Picking the sets you gave, most of the old renamers are not around anymore and i've no idea of what "MCA" represents. According to our info, it might be the abbreviation for a German scene group named "The Magic Cracking Association", or at least that's what happens with Amiga. For STCS i have no idea and so on for the others, you might want to help me out in this too by providing me the information (and a screenshot), just like TKaos and mai do, you can check one topic from mai named Amiga Scene Groups around here. I will give you more details about this part if you want to help with it too. If not, fixing existent sets is already a great contribution

Good luck and don't hesitate in contact me.