-a divider would be used to seperate a water feature the substrate to keep the substrate from being too soggy and the water getting dirty or it can be used to keep 2 species seperated if they don't get along (like a larger salamander species and a smaller one), here is a related article:
Caudata Culture Articles - Setups With Dividers
-im not really sure as i haven't used it myself, im sure most silicon brands work the same way and should be used in the same way, i may be wrong so i would wait for a more knowledgeable member to come along for your silicon needs.
-i use coconut fibre with my tiger, when i get the money im going to make a mix of 50% coconut, 25% top soil (organic), and 25% sphagnum moss (brick) and here is a link about substrates to use with terrestrial species:
Caudata Culture Articles - Vivarium Substrates
-better yet, i have the caresheet which covers all suitable woods and which ones aren't :
Caudata Culture Articles - Wood in Vivaria
-most hardy plants will work, as it needs to be able to survive the stomping/burrowing/whatever else that your salamnader will put it through, you could alternatively leave the plant in it's pot, specific examples are ferns, moss', you could also look at your sals natural home and the plants that live there, fake plants will also work.
-i have never seen the side-by-side comparison of sals with treated water and sals with tap water, i've always played it safe and treated my sals water beforehand as i know chlorine can wreak havoc on my own eyes, for most sals though they will use direct water rarely and when they do they will use it to go to the washroom instead of a drink, im sure tap water would be fine if you can't get your hands on some de-chlorinator.
-im sure most light sources will work fine, you could go all out and spend a couple hundred dollars on the "deluxe-super sun ULTRA package" but i don't see the need for them, sals won't need any light (i wonder what a pitch-black environment would do to a sal?) to be happy, the light would be so that you could look into the tank and oggle your sal (i know i oggle my sal a lot, he/she is so pretty) and to keep the live plants lively. just for reference my plants (some local moss and a lovely local vine plant) do just fine with the lightless corner (some sunlight, not a lot) and they grow despite my sals constant stomping and thrashing as he eats.
the questions are fine i enjoy helping out a fellow member where ever i can, i may not be an expert but i do know what works for me and what has worked for others before me, and besides we all want the best for our 'slimey' little friends (note: not slimey).
also here is an article related to building projects if you want to give them a look and maybe an attempt:
Caudata Culture Articles - Vivarium Building Projects
(if it has water in it you could try it without the water)
