I have had it out with a couple members here about the addition of bugs to the tank and most say its a good thing an i can agree to a point in regards to Worms, Wood Lice and Pillbugs. The one thing that always bothered me is now your tank has to be set up to handle this new bioload and adds i guess what we can call a 4th dimention to your tank care. You need to know if one population of insect (A) will overrun your Viv or will insect (B) work as population control, Unless you know exactly what your putting in the tank i wouldnt add any " wild found " mats to your Viv the variables are great and many in this situation. Now for your questions
(1) Ants and spiders are good ways to keep pests other then themselves out of the tank but thay will both eat your crickets or whatever you feed the FBT's and depending on the ants thay may also destroy your plants, but both will most likely not alow for any other type of insect to thrive long enough to do any doog for your Viv as in worms and pillbugs.
(2) As your Viv cycles the necessary bactiria and fungus will all balance out no need to add your own. You can bake the dirt and litter in the oven and wood can be soaked in a mild bleach / water solution for a couple days just be sure to soak it in a larger amount of water and rinse it very well before adding it to your tank.
(3) Imho, nope, Kill'em all!!!
(4) Like i mentioned before, if you no not what your getting dont use it, bake those suckers as well.
(5) Moss may eventually grow on everything you add due to enviromental conditions within the tank or may not, I would try to figure out that kind it is and then figure out if you want it in your tank or not, it may grow like wild fire or may die off.
A couple other things you may want to take into mind is the area you got this stuff from and the use of chemicals in the water and surrounding woods, the native insects and the amount of light within the area your searching as this will tell you what conditions the plants and moss's will need to survive ( ie low light or high light, dry or waterlogged floor), is it neer a huge leaking nuclear reactor as you wont want your insects eventually eating your family dog or kids

. i guess the moral of my story is when somebody asks me whats that thing im my tank i want to be able to tell them what it is and not just blurt out " oh that? why it a native "randomus wingdus bothermeloticus"..... god its 5 am and im getting retarded, i hope this makes sence and helps ya