re: Please help me with proper leader selection
As you've seen, there are many different opinions about leaders. Over 40 years of fly fishing, I've tried them all. But, I always come back to tying my own based on the size of fly line I'm using and the size of fly I'll be throwing. My target is to start with stiff mono (Maxima Chameleon is what I use) that is about 2/3 the diameter of the end of the fly line. I use four feet of that size. Drop down .004 and knot in a foot of transition mono. Then I drop down another .004 and add four more feet of that size. Whatever tippet size I need for the fly size, water and wind conditions is then added to the end of nine foot leader. I usually add 24 to 30" of tippet.
Lines 3 and under usually start with .015. 4 and 5, around .020. 6 and 7, .022.
Spey lines, usually start with .024.
But for easy--buy 9' prepackaged leaders and use the loop they come with to connect them to your fly line. If the line doesn't have a loop, have your local fly shop nail knot the 8" of .020 or .022 to the fly line and then loop the leaders on. Buy enough tippet to replenish the leaders after several fly changes.