Nobody has inifinite space (or the infinite time/money needed to utilize it if they did). By using pseudo-mushroom and double deck construction I can use the single garage stall 12' x 22' and overlay the back of the garage with an upper level area 24' x 13' (a portion of this area overhangs the back of the double stall where the family cars are parked and must be suspended from the beam crossing the ceiling.
This is just enough space to model in On3 (of course the plan could also be done in Sn3 or HOn3)
The dual level approach suggested the mountainous part of the SPC be modeled. Since I like mountains this works great.
Thus I'll be modeling the SPC from Los Gatos south to Santa Cruz plus the Boulder Creek branch line. The era is 1895 at which time the standard gauging process had just reached south to Los Gatos. Also in 1895 both the Boulder Creek and Laurel areas were generating tremendous amounts of lumber some of which was sent to Santa Cruz for loading on ships but most of which went north to help the building boom going on in SF, Oakland, Alameda, and most other locations around the bay.
To meet druther #2 a staging area is provided representing the towns/cities north of Los Gatos. Trains moving south from Alameda/Newark/etc pop out of staging at Los Gatos. Trains headed to Alameda/ Newark/etc leave Los Gatos going north and disappear into staging. The staging is set up on a reverse loop with some stub ended sidings and some double ended such that a passenger train from Santa Cruz can be temporarily parked in staging for some time (simulating the trip to Alameda, turning around, and heading back south) before "looping" back to Los Gatos (without needing a wye, turntable, or significant operator attention). This helps because the SPC ran three through passenger trains each direction every day. Plus locals. Plus through freights.