Where was the stand-alone model for simulation-based MPC proposed first?
The standard (stand-alone) definitions were developed over many years, including the original GMW, Beaver, Goldwasser-Levin, and Micali-Rogaway. However, the standard definition used today is by Canetti, and was published in the Journal of Cryptology in 2000. That paper also proved the modular sequential composition theorem. Here is a link to that paper: https://eprint.iacr.org/1998/018.

It is worth nothing that the above paper actually only deals with the honest majority setting. However, the changes needed for a dishonest majority are minor and straightforward, and make no difference to the proof of the modular sequential composition theorem.