Hmm....
First I have absolutely zero idea what you are talking about with cheese and cooldowns. If you are hiding somewhere not attacking because you are waiting for your cooldowns to end, YOU ARE NOT CONTRIBUTING TO THE FIGHT. You are leaving your team down a person, making success less likely.
Sounds to me like you've founds some kind of edge case where someone can be boring and exploit a game at the cost of making it completely unfun for THEMSELVES. Whoop-de-do. That, to me, does not seem like it is a problem which needs fixing when the cost of fixing it means that using sneak or invisibility in a normal way is not allowed.
***
1) You cannot enter sneak if you are within a 1-1.5m radius of an enemy. (Maybe different radii for different enemies i.e. zombie is dumber than human).Well, given that basic attacks cost 2 AP, Sneak costs 1 AP, you get 4 AP per turn and moving will cost you 1 AP or more to reach an enemy, That means a Rogue would need to start 5 or so meters nearby an enemy, outside of any sight lines, the enemy can not move and MAYBE the Rogue can move to just outside of the circle with 1 AP, Sneak with 1 AP, move into the circle with 0 AP (assuming there's a free fraction of a move left), and attack once, after which they are out of AP and will take a beating.
The Guerrilla talent, already awful, is reduced to being useful ONLY for Snipe archers and will need to be deleted completely.
2) Enemies rotate to face you as you move. You have now completely eliminated backstabbing from happening AT ALL except for Vault, which doesn't even require the Back-Stabber Talent.
3) Enemies look for you. "Where'd he go!??!"This is the best solution of the three, but only if not combined with anything else. It also does have the similar issue of the others in that if the enemy starts looking around for you, it means that you are essentially forbidden from sneaking at the end of your turn.
Because once again, 2 AP to attack, 1 AP to Sneak, which leaves 1 AP for moving, and you have to spend that either to reach your target or to leave, but you can't do both. How many combat encounters have cover which is within the 5 meter distance you can cover with 1 AP but an enemy standing right beside you cannot when they are actively looking for you?
Regarding the actual Invis skills, in my humble opinion, I think one or all of these nerfs would be fair:
1) Impossible to go into invis while Flanked.
2) Impossible to go into invis within touch Radius.
You mean, the situations in which a squishy melee-range character MOST DESPERATELY needs to escape from enemies who usually have "Attack of Opportunity"?
Your ideas boil down to "I think Rogues should be completely useless. Delete Sneak and Invisibility from combat completely".