Follow your buddy's advice. Don't take the chance. Jack stands are dangerous enough when the car is not running.
That said, if you have a pair of ramps, get two more. Get one end of the car up on ramps then raise the other end and put ramps under it. Still not the best, but much safer than jack stands.
The simplest and safest, is to get out your trusty flashlight for seeing into dark places under the car. If you have any appreciable leakage, you'll see it on the floor pretty quickly.
Oil filter and cooling lines (if any) are the most likely leakers. There shouldn't be any water leaks, if you put the hoses on properly and didn't ding the radiator or forget a thermostat gasket. The only thing left is the fuel line and that you can see from top side.
If you have or are going to prime the
oil system with a drill motor, there is opportunity to spot big leaks while doing it. Other
oil leaks probably won't show up until internal oil pressure is at operating levels.
Al