How often do armored trucks spawn in GTAV Online

There are only a few single-player missions that effect the in-game stock market, and they're mostly concentrated around the Lester assassination missions. The companies involved in the heists, including Vangelico, do not appear to have any useful/exploitable effect on the market.

The advice I followed to track the events that effect the market in single player is on this page. Lester does a pretty good job of informing you how to invest during these missions, though. If you wait until after the final heist to do as many of these missions as you can, you stand to make a pretty good profit.

I use the entrance to the subway construction site located under the overpass - it's a construction tunnel; a rough dirt ramp leading down underground. Police will only enter from the tunnel mouth and never come up from the subway side.

I tend to crash a few cars into the tunnel mouth which wind up blowing up. It's not a sure fire way to block the police, but if you take cover behind an upright girder bracing the wall just down the slope, you have an excellent spot to shoot them as they come down.

You can try the same thing at the opposite end - it opens into the storm drains but the entrance is under a raised bridge which gives the police excellent firing position on you, as the tunnel mouth there is very wide open. You can however shoot down helicopters from here with the high end sniper rifle.

When you want to lose your stars, it's almost trivial to run down into the subway and they will quickly lose sight of you.