I am very pleased to hear about your interest, to take part at the delta Sco monitoring. Actually there have been some amateur observers from the southern hemisphere, but they have been unable, to provide spectra this year.
Because of that, it would be really great, if you could take part. The upcoming periastron passage required a high frequent observations in different aspects.
Concerning your questions, which grating you should use, I would say, both, the 2400 and the 1800.
If you would prefer the first case, this required changing the wavelength adjustment. I am working in this way.
On the other side the usage of the 1800 grating is a little bit more comfortable. Only the line profil informations are less in detail.
If you could contribute brightness measurements as you mentioned, that would be an additionally advantage. So far I know, there are not so many observers, who consider this important aspect (except Sebastian Otero in Argentina).
Regarding S/N, you should achieve a level of approximately 100 in minimum. Then the substantially informations are available.