I would stay away from the Bear Montana, pretty rough.
Being left handed limits your selection right off the top. Are you left eye dominant also? If you are right eye dominant, buy a RH bow.
My advice is find a place that you can actually shoot a bunch of different longbows. You will soon figure out what you like.
Do you have traditonal shop close by? Is there a traditional group of guys close to where you live? Most Traditional guys are extremely helpful. Pick up a copy of Traditional Bowhunter Magazine. They have a whole section dedicated to Traditional archery clubs.
I know Black Widow and Robertson will let you test drive bows.
My personal advice for starting:
A lighter weight bow 50-60 lbs.
A longer bow 64-68" will have increased stability.
A heavier riser will be more stable in the hand.
Use a heavier arrow 10-12 gr per pound of draw weight, material not important. This will also help with stability as the arrow will absorb more of the bows energy.
Another thing I like is the slip on quivers like selway etc. This adds mass to the bow and makes it more stable when shooting. This is a personal preference.
Arrow spine is going to vary depending on length and how centershot the bow is.
Oh, and BTW, this traditional thing is very addictive and a very slippery path to go down. You will never be the same.
Or let me know where you live and I can look one up when I get home. PM me if want.
