Were the members of MM involved in music before this band formed? What are past members doing now?

Mr. Manson was working as a music journalist, and had a few pieces published in local S. Florida music papers.

Daisy (Scott Mitchell Putesky) stated in his "Guitar School" interview that he had played in four or five bands prior to joining Manson, "only a couple of which did club dates." The only one whose name is known, a duo called India Loves you (with Cindy Deats), was described by Daisy/Scott as "psychedelic folk combined with Sonic Youth's noise". He has continued to work in music since his departure from Marilyn Manson; his latest work is under the name Three Ton Gate.
In April/May of 1998 it was announced that Scott had joined Jack Off Jill as their new guitarist, replacing the departing HoHo Spade. His name in Jack Off Jill is SMP.

Twiggy was a member of south Florida metal band Amboog-A-Lard - playing originally rhythm, then bass guitar - before joining Marilyn Manson. (While with the Amboogies, he won the 1992 Slammie Award for Best Rhythm Guitarist; however, he's credited with bass on their 1993 CD "A New Hope.") And he had a busy week on the NiN/MM tour in December of 1994: in addition to his regular bass chores with MM, on 12/8 he did a one-night-stand with Nine Inch Nails, filling in for the injured Robin Finck; and on 12/10, on New York's Bleecker Street, he played his only gig as a member of Dee Snyder's Sick Muthafuckers.

Ginger is said to have played in a number of Las Vegas bands, and to have 10-11 years' experience as a drummer, but we have no further info on this.

There's no info on musical efforts of Gacy prior to joining Marilyn Manson.

Zim Zum played guitar for Chicago based band Life, Sex and Death, for a short time, joining after they had recorded their album.

Bassist Olivia Newton-Bundy (Brian Tutunick) went on to become the vocalist for Collapsing Lungs, which broke up in late 1994 or early 1995. Various members continued with other musicians under the name L.U.N.G.S., while Brian went on to found Nation of Fear, his current band. Check out their website for some early MM & the Spooky Kids photos and further info.

Original keyboardist Zsa Zsa Speck (Perry Pandrea) is still floating around the South Florida music scene according to recent reports

Gidget Gein is in New York, and has just released the first CD for his new band, the Dali Gaggers.