Hey. A lot of it is just going to based off your opinion. I assume you've seen some of the photos and comments I've made on other threads regarding the conversions. Here is my 10 gallon rack. I have 2 on the bottom at this point and still need to do 2 more
I have computer fans on order for the middle and top level because they get too warm during the day.
Metal hinges Vs a living hinge runningthe length of the door
I 2 metal hinges on my tanks. Do I really like them? A little. I could probably look longer and find something I like better. Downside to using the metal hinges is that silicone doesn't like to stick to the plastic frame of the tank. The epoxy will stick, but doesn't really like the plastic rim either. I use loc-tite brand epoxy for plastics. I also have started sanding the plastic under the hinge so the epoxy has something to grab.
I personally wouldn't want a long hinge. Honestly I think the hinges look bad as it is.
Latches Vs some of the slide locks shown on some threads
Latches can be nice. Slide locks can be nice. I've tried with a couple and found that when I start pinning bamboo in the tank it moves the door/frame enough to unalign my latches. I made a frame for the glass door and make sure it doesn't fit real tight, but isn't loose. Most of the doors actually hold themselves shut. On the ones that don't, I use painters tape. Doesn't look good but works good.
I had also tried some hasps with some U shaped pins. Most ended up popping loose. So I just gave up on that
Framing all the panels of glass Vs just sanding the edges down
You can see the U shaped pin and hasp in the second picture. I use silicone and put a bead on the channel that the rubber thing for the screen would sit in. (Can't think of what it is called) I get the glass cut to size to where it will sit in that channel perfectly. I also use a bead around the outside lip of the glass and smooth it out(gently-don't cut yourself). I have found this to work VERY well. The silicone holds the glass to the frame well and the extra bit will keep you from cutting yourself.
Vent at top of front conversion kit Vs removing glass top and using vent there
I have not tried a vent in the front of the tank at the top. I think this would look bad. Granted it will make your conversion very easy. WHen you rotate the tank up and need to get the new "top" piece of glass out, it isn't easy. I bust the glass and take out the shards. Last 4 tanks I got I ended up only being able to use 2 because I more or less destroyed 2 of them.
The other downside to a front vent vs. a top vent is that heating the tank will be more challenging. You won't be able to use heat lamps if you have a front vent. With cresteds you won't have to worry as much, but I keep Phelsuma and they like it a lot warmer. I know that when I mist my geckos the tanks go upwards past 90% humidity for a while.
Silicones Vs epoxies (brands youd suggest)
I use the loctite brand epoxy and whatever the regular silicone that home depot sells. Silicone 1 or 2.