Questions for Northern Blue tongue Skinks!!

[Fotizzile]

ok so ive decided to just post all my questions in one post instead of spamming the entire forums with different questions. im getting a northern blue tongue soon and i have the enclosure already ready. at the moment i have a indo blue tongue skink using the enclousure, so in order to keep the humidity up i have to spray the tank every day. the substrate i used is cypress mulch mixed with cocunut fiber. i dont use a heat lamp but instead a undertank heater (i avoid spraying that side as i fear it might crack the glass). my enclousure is a 90 gallon aquarium ive had and my heat pad said its only good for 60 gallon tanks (not sure if its reptile enclousures cuase my tank is 4 ft by 18 inch). anyways with my backstory here are my questions.

1) humidity lvls stay around 50-60 without spraying, ive heard that i shouldnt have wet cyprus mulch in my tank with northerns. is this true and why?
2) hot spot fluctuates throughout the day hitting a high of 99.6 and lows as low as 86 F is this acceptable?
3) i use a tile and light substrate on my hot side. the tile doesnt get as warm as just having light substrate but my indo seems to prefer the tile then the light substrate. is it important that i get a heat lamp or can i just use the heat pad?
4)i heard somewhere that a bts will be more skittish and agressive if it smells the sent of another bts. that being said what would be a efficent way to get rid of the scent of the indo? pet store owner told me i should bleach everything and get rid of all the substrate but ive only had the indo for a short while and this seems a bit over the top. can i simply remove a little of the substrate where i know the indo spends all of his time and then just spray the tank down with one of those reptile cleaners thats suppose to deodorizer the tank?

the questions are all over here but i tried to make it easyer by numbering them. any help would be appreciated! thanks!

[splashy07]

I would clean the entire tank and start over. Cypress mulch is not a problem, I've used it for northerns with no issues.
I prefer coco husk and repti-bark though. I have used aspen but it is too dry and dusty and they were having difficult sheds.
Also, I do not like under tank heaters on glass. When they go bad they can overheat and burn your lizard. If you are going to use one, use with a thermostat. Overhead heating is preferred and more natural. They do like to bask before they go in search of food.
No damp cypress or any substrate unless it is confined in a humid hide for shedding purposes.
Your cool end is a bit high but I don't think unacceptable, if your lizard doesn't like it he will be unsettled. It gets hot in my apartment in summer and they don't seem to mind, I just switch their heat lamps to LEDs.
I would use an overhead lamp though, it will stimulate natural behavior.
As far as your skink smelling another one, never encountered this issue, but again I would just start over.
Good luck with your new pet! Be warned they are highly addicting!

[alichamp]

Sorry I a bit confused. Your new bluey will have its own enclosure right? You are not planning on adding to the enclosure with your Indo are you? And so where are the two enclosures for the two animals coming from?

I suggest that you put the northern in the new enclosure rather than one used by another animal. Otherwise, it is not just the scent but the risk of transfer of any diseases infections or other things. A really good thorough clean out using a bleach solution will be needed before using for the new animal.