Help me with my Board Layout and Stealth Mechanics

Encounters
I'm assuming that your intent is for encounters to be sporadic and not occur every time a move is made. And that once an area has an encounter, that area is then cleared.
Perhaps, instead of putting the cards on the encounter areas, use a token. When a player enters the area, draw an encounter and remove the token.

Some ideas:
• Make a group of spaces represent a single encounter area. (Surround them with a colored border, perhaps) When any of the grouped spaces is entered, draw an encounter. This way you can make encounters occur periodically, while also preventing a player from going around the encounter space.
• Arrange encounter spaces like a web or net, so that encounter spaces will have to be crossed eventually.
• Every space is an encounter, and include encounter cards that are blank.

Stealth
The big question is what does the stealth accomplish?
If the answer is mostly to prevent doing stuff to a player that your character wouldn't be able to see, then the perception range should be fine.
If the answer is so that you don't know where the other players are (because there is strategic importance) then here is an alternative:
Use "decoy" tokens. Since players only control one unit there won't be too much bookkeeping.
It works like this: Every player has 3 or 4 placeholder tokes that have a letter, and their actual unit is off the map. Somewhere they have a letter written down, and this letter is the "real" unit, the others are decoy units.
• A player may reveal the real location of his character at any time, and must reveal himself to perform actions or do encounters. (remove any decoys, and replace the "real" decoy unit with the players character)
• If a decoy unit enters an encounter space, the encounter is not triggered and the decoy is removed.
• If an opponents REAL unit gets close to a decoy, he may force that unit to be revealed. If it is a decoy, remove it. If it is the real unit, place the actual unit in its place.
• Decoy units may not reveal other decoy units.
• A player may "hide" his actual unit on the board and replace it with multiple decoy units. (And record which letter represents the real unit)

So Alice decides she can head towards the fruit trees to get food, or go to the abandoned mine to find some tools, or head to the stream for water, but she doesn't want Bob to know in advance where she is headed.
She decides to go to the abandoned mine, and removes her character and places decoy units A, B, and C in its place, secretly recording 'B' as the real unit.

Over the course of a few turns she move the decoy units in different directions.
Bob is not sure which unit is real, and send his decoy units to intercept her - but he is guessing she is going to the fruit trees - and sends his real, but hidden, character that way.

At some point, one of Bobs decoys is close to Alice's decoy 'C'. However, since neither represent their actual characters, no one can reveal the others' decoy, but neither player can be absolutely certain that the other isn't their true location.

Next turn, Bob's actual character is in position to see Alice's decoy 'A', so he elects to reveal his true location, removing his decoys and putting his character on the board. Having done that, he can now use his character to look at decoy 'A', and he finds that it was indeed just a decoy. He now has a pretty good idea where Alice really is, but he's out of position!

Alice now reveals that 'B' is the true character, and gains some tools at the abandoned mine.
Next turn, Alice decides to re-stealth her character. She removes the playing piece and places decoys A, B, and C in the same space, secretly recording that the real unit is now 'A'. She can now secretly move to her next objective.

Finally, as to paranoia and theft of an idea: There isn't much financial incentive to steal a board game idea. Ideas are the easy part and they are a dime a dozen. The hard part is making that idea into a polished game.
Most boardgames aren't exactly cash cows these days, so really, the risk/reward ratio doesn't lend itself to idea theft too well. There's too much work to do to make and idea into a workable game to have the final product encumbered by even the hint of copyright/trademark claims.

Say I have a stealth rating of 3 and you have a stealth rating of 5. That means that I get to move 3 instances of myself around and you get to move 5 instances of yourself around. These pawns behave like normal characters, but when our characters meet, we simultaneously declare if they are real or decoys (by revealing cards?). When one is revealed to be the real one, all others are lifted.

If you have only one instance and you are not observed, you can spawn off other instances to the limit of your stealth.

Consider this: I start my turn in one specific place. I have Stealth: 3. This means that I get to spawn off 3 instances during my move phase. I move one instance to the north from where I started the turn. I move one instance upstairs from where I started the turn. I move one instance to the west into a shed from where I started the turn. I take no actions that only my real instance is permitted to use, so you don't know which one is real.

On your turn, you spend three energy to activate the trap in the shed. I decide at that instant that my shed instance is a decoy and remove it from the board. The rest of your turn doesn't engage either of my remaining two instances.

At the start of my next turn, I decide that my upstairs unit is the real me and lift my instance to the north. Now the entire process starts over again. I can spawn up to three instances, etc., etc., etc...

Core Ideas:
* You do not have one unit that is secretly the true you.
* If there is more than one instance of you at the start of your turn, you must lift all but one instance. The remaining instance is the true you.
* Most of the actions an instance can take can only be taken by the true you. If you take one of these actions, you must lift all other instances of you that are currently in play.
* When something other than you (another player, a board event, etc.) engages an instance of you, you must decide and declare if that instance of you is the true you. If it is not, you lift that instance and the engagement fails. If it is, you must lift all other instances of you and resolve the engagement.
* During your turn, you may spawn off instances of yourself up to the limit of your Stealth rating. These instances of you start from your current location and follow all of your normal movement rules.

Etc:.:
* If I were implementing this, I'd let decoys move and reveal what's in their rooms. I would not allow decoys to fight or otherwise affect their environment in meaningful ways. I probably would not let decoys pick up or carry objects. I'd reserve fighting and such for the real you.