I'll take a stab at some of your questions.
1. It is legal to have (you do not need a PAL/RPAL)...not legal to transfer (in general). There are 1-2 sources that obtain them legally for resale...and those specific ones can be legally transfered to you the end user. It's at best a bit murky. I suppose technically if you do obtain a non-ancient one (Pre 199X something)...you're in possession of an illegally imported item and that may or may not mean something to you.
2. Opaque vs. Transparant (or some degree of tranparancy): "clear"/"semi-clear" items came about since a main point that classifies something as a replica is that it is not easily distinguishable from the real item. Obviously having the receiver transparant goes a long way in making that distinction (BTW...doesn't matter if it's blue/pick/camo/black/etc....it's either "transparant" or not). Legal? see point 1.
** General note **
The dummies guide to it is.....right or wrong/common sense or not, with few exceptions it's not legal to obtain/trade/transfer these things...and to do so is a decision you have to make.
One thing is absolute....it is NOT worth it to try to smuggle/import/order in from out of country these things yourself. Lost monies aside, the legal charges can be significant and long lasting. Every year there are guys who try...and fail.
3. BEWARE of some of the asian market gear. A $20 Delta Elite vest might seem to have all the MOLLE/features that you want...but when the stiching falls apart, the poppers rip out of the pouches and you find that the spacing of the MOLLE is all uneven you'll be left with $20 of scrap material. After spending lots of money on various gear over the years I'd sum it up with........set a budget, buy real stuff if you can afford it, buy Pantac if you can't. Quite honestly, much of the PANTAC stuff is just plain a good bang for your buck and will likely hold up to all the rough abuse that 95% of the players can dish out at it. Real stuff is nice though...
Hope that helps more than the inevitable "go get Age Verified" messages you'll get.