Main thing is look at the minimum system specs, make sure you have at least that. If you intend to run on a laptop double the minimum specs. Full list of TS12 built in routes is easy because there aren't that many;
Balezino - Mosti,<kuid:354694:1009>
Debrecen - Nyiregyhaza,<kuid:9999:20010>
ECML Kings Cross - Newcastle,<kuid:154322:100362>
Mojave Sub Division,<kuid:487560:69000>
Municipal Transit Railroad,<kuid:82412:1152>
NEC Wilmington - Philadelphia,<kuid:56511:100018>
Norfolk & Western - Appalachian Coal,<kuid:453099:100086>
Southern China,<kuid:521433:1079>
Springfield Industrial District,<kuid:447264:1035>
Category locomotives built in I get 213, rolling stock 443, either way too many to list. Sessions I can do since there are only 28 built in;
Acela,<kuid:61119:65008>
Army operations,<kuid:9999:20016>
ATSF #991 East,<kuid:487560:100004>
Balezino - Mosti, Day Passenger,<kuid:354694:1028>
Balezino - Mosti, Night Passenger,<kuid:354694:1024>
Coal to Gong Tang Power Station,<kuid:447264:1201>
Commuter train,<kuid:9999:20013>
Eastbound Coal Train,<kuid:447264:1209>
ECML Christmas Mail Train,<kuid:61119:65007>
ECML Hull Executive,<kuid:61119:65005>
ECML Lincoln Relief,<kuid:61119:65006>
Elevated Railroad,<kuid:82412:1155>
Helicopter,<kuid:82412:1156>
Learning the Line,<kuid:9999:20015>
Logging yard,<kuid:9999:20012>
Mojave To Bakersfield,<kuid:487560:100002>
Mosti - Balezino, Day Passenger,<kuid:354694:1010>
Mosti - Balezino, Evening Passenger,<kuid:354694:1005>
MT TUZEP,<kuid:9999:20014>
Multiplayer Session,<kuid:447264:1213>
Passenger Service,<kuid:447264:1202>
The DPU Push,<kuid:487560:100001>
The Walong Stall,<kuid:487560:100003>
Tutorial 1 - Introduction,<kuid:447264:1021>
Tutorial 2 - Driving in DCC mode,<kuid:447264:1037>
Tutorial 3 - Cab mode driving with Electric Train,<kuid:447264:1022>
Tutorial 4 - Cab mode driving with Diesel Locomotive,<kuid:447264:1040>
Westbound Merchandise Train,<kuid:447264:1210>
Looking for a larger selection of built in routes, TS2010 might be better;
Avery - Drexel,<kuid:82412:1338>
Bad Schandau - Decín,<kuid:46162:1455>
Banks Heath,<kuid:-18:1846763756>
British Midlands,<kuid:-1:100000>
British Midlands 2,<kuid:-3:10172>
City and Country USA,<kuid:-1:100927>
City and Country USA 2,<kuid:-3:10174>
CN Holly Subdivision,<kuid:107727:1019>
Conrail Lincoln Secondary,<kuid:107727:1144>
CSX Saginaw Subdivision,<kuid:107727:1062>
Demo Modula City 2004,<kuid:60349:100002>
Detroit Connecting Railroad,<kuid:107727:1008>
Downtown Traction Company,<kuid2:69871:100723:1>
ECML Kings Cross - York,<kuid:447264:1019>
Electric Commuter,<kuid:-18:1004>
Glasgow to Falkirk,<kuid:523:1011>
Harbor Master,<kuid2:69871:100709:1>
Harlem Line,<kuid:-12:1002>
Hawes Junction,<kuid:69379:100411>
Highland Valley,<kuid:523:1013>
Highland Valley Industries,<kuid:-3:10173>
Iberia Interior 4,<kuid:86311:697992>
Industrial Wasteland,<kuid:63015:100019>
MagLev Project 2006,<kuid:45707:100030>
Marias Pass Approach,<kuid:46162:25103378>
Metropolis - Modula City,<kuid:60349:100001>
Modula City Custom Map,<kuid:60349:100007>
Niddertalbahn,<kuid2:208598:100050:6>
Northbay County,<kuid2:44700:800045:1>
Outback Australia,<kuid:-1:100835>
Outback Australia 2,<kuid:-3:10176>
Port Ogden & Northern,<kuid2:69871:100334:1>
PT Dresden-Nuernberg Demo,<kuid:151900:500530>
Queensland,<kuid:-18:1006>
Razorback Classic,<kuid:46435:600060>
Roanne 07,<kuid:523:100009>
Robe River Iron,<kuid:-18:1001>
Robe River Iron,<kuid:3801:20000>
Rosworth Vale SP2,<kuid2:5562:20011:2>
Springfield Industrial District,<kuid:447264:1035>
The Black Forest,<kuid:-1:101233>
Thueringen romance route,<kuid:121616:1001>
Tidewater North,<kuid:47119:1015>
Tidewater Point Rail,<kuid:9000:100341>
Tidewater South,<kuid:47119:1013>
Tire Bouchon 07,<kuid:523:100007>
Toronto Rail Lands 1954,<kuid:70337:678419719>
Wadalbavale Line,<kuid:61119:9092751>
Wadalbavale to Karrah Bay,<kuid:523:1023>
Winter in Germany,<kuid2:143919:27565:1>
Winter in the Alps,<kuid:-1:100858>
Wirtschaftswunder DE,<kuid2:300062:1082:1>
With 137 sessions, 463 locos, 724 rolling stock.
Lots more free stuff on the download station, no guarantees on quality or completeness since that's a matter of individual taste.