Actually I'd highly recommend a Li-Po alarm. It plugs into the balance lead, and sounds a buzzer when any cell reaches the voltage you've set.

Practicing trimming with the sim is a great idea.

Also it is not an uncommon practice to have someone help you trim. Particularly if the plane tends to dive, it can be tough to get off the stick and on to the trim switch repeatedly while keeping the plane in the air. If someone can give you up trim until it is close, things are much easier.

Something else to practice with the sim would be recovering the plane from a stall, or unusual attitude.

With the real model, keep it close but keep enough altitude that you can have time to recover from a mistake or two.