Set up your schedule in the schedule library. In driver set-up, use copy commands from and select the schedule. You use the copy command repeatedly if you need to do the schedule more than once. The last copy command would be the schedule to return the train to its depot position.
Where they stop is down to you and where you schedule them to go. Once a schedule is complete, they just stop. No command or rule will automatically send trains to a location.
They would all need an extra schedule to put them there. Use the schedule library to set up your schedules and separate...
You could use an invisible speed sign on the main line that tells the train what speed to use at the junction. The invisible speed sign can set different speeds for each diverge.
Which asset? If at some point you had a DLC asset installed on your route with a newer version and then saved it, it would show as not available on the DLS if you tried to redownload it.
You could use a TM on each of the two tracks in the passing loops. Name them something like "Loop 1 (1)", "Loop 1 (2)". Loop 1 (1) on the main track and Loop 1 (2) on the siding. Do the same in each Loop, but increase the loop number like "Loop 2 (1)" ", Loop 3 (1)".
A driver command, Drive via...
It depends on the speed of the train and the distance the first trigger is away from the crossing. You can use more than 4 triggers on a track.
First trigger set half a mile away, set for priority 1 only. All fast trains using priority 1 will trigger the crossing. Second trigger 1/4 miles away...
Use an AJS invisible station. This one <kuid2:122285:3401:22> AJS Invisible Station 1T 3.5 is short, but passengers can be curved on either side and length can be set.
Some scenic splines, like fences, had been created as track splines in the past. Check CM for missing assets; they should still be available to download or at least show what they were.