Question
Is it true that the more the well gets usesd it is better for it?
What do I need to pump water from the lake that has a 75ft rise and a 600 ft run for watering garden & lawn area?
What size water supply line to provide pressure for 1/2" hose?  Do I need to consider water pressure & volume in a pump and supply line?

Answer
Thanks for your question.
Somewhat true. If your well is in good condition and in good water. You won't "hurt" it by using it. To some extent, the reverse can be true. If a well sits for long periods of time with no use, the screen can get a bit plugged. That depends on the water quality.
Using the lake water is a viable option. You will need a pump capable of producing 75+ PSI. Your going to loss 32 PSI just getting up the 75' rise. The pump will need to be a 2 or 3 stage and 1-1/2hp or 2hp. A 1" pipe would provide limited water to your system, but you really should run an 1-1/4" or larger line from the pump to your system.
I can help with a pump size, but I'll need to know what State your in or what manufacturer of pumps you have available. Each area of the US have different pump manufacturers which are predominant. You don't want a pump which is had to find or difficult to get parts or service. If you have neighbors with sprinkler systems, ask what kind of pump they have. It will give a me much better direction for pump selection.

Matt