It depends, mine lasted for 3 years and 6 months. So I'd say between 3 to 4 months.
you have to go through enough story line to save the mochi's
You have to download PS, PS2 emulator and MR roms to play on PC.
My Monster Rancher only runs on Android and IOS.
Truthfully, there is no "best" when it comes to the MR franchise, as there are many different types with totally different fighting styles.
When I first started playing MRA2, I regenerated a full-blooded "Antlan" and began to train it. I've found that these type and "tiger" types are easy to handle and, with a high enough POWER stat, can knock out ANY monster with just a few "fire punch"es or "scratch"es. After you get you POW and DEF up to 500+ and 400+ respectively, you shouldn't have trouble with anything all the way up to S level tournaments.
Also, CHOOSE COACHES WISELY! They make all the difference!
You don't catch monsters in Monster ranch. You tame them by beating the monster.
I hard about a game similiar to Monster Rancher called Lusus Tales of Atnuh.. Supposed to be 2 coders using the included art.