Is there any point to making Skywalker as hard to kill as possible?

Maybe +Agility R2/Stealth/and even elusiveness

Squadron him with 3xRookies?

Is it a good idea to do something like this in tournament to make him surviveable saving lots of points to late game?

I think you described the point of doing this yourself. 36 points is a lot for an X-wing, but it would be difficult to hit him. Not impossible though, as he would only have a standard 4 defense dice at normal range 1-2, assuming you use R2-F2 every time. Additionally, if you use elusiveness much you are stressed, which is bad for an X-wing with limited green options. So that may be 2 points better spent elsewhere.

All it takes is a TIE Interceptor or Firespray at range 1 to have a good shot at breaking your stealth device. (Or a Falcon or X-wing of course in mirror match).

It's not bad if played well, but probably not a tournament-worthy option I think. He will probably be ignored anyways until last, I would think, but I guess that was your strategy.

Nevertheless, 4 X-wings is never a terrible build, so try it out and have fun.

You would probably be better off with a similar setup on Wedge. With Luke, he likely isn't going to get shot until the rest of your list is dead, and at that point, when all that fire gets focused on Luke, he will go down regardless of the stealth device.

If you went Wedge, Push the Limit, R2F2, Stealth Device you'd be able to get the extra agility as well as target lock or focus plus you'd be causing extra damage. You'd force your opponent to either shoot at the hard to hit Wedge, or leave Wedge alone and focus on your easer to hit models.

I find the best way to get your mileage out of Luke is to play him very aggressively. I will run him like this.

Luke (R2D2, Marksmanship, Shield Upgrade).

When playing, I will fly straight into the enemy with Luke, trading nose-to-nose Range 1 shots with whoever. I use Marksmanship to hit hard, and rely on the Force to keep Luke alive. I then pull straight greens as I fly past to open up the range and recover shields, then green turns and / or hard turns to get back in the action, just so long as he has full shields on the next pass.

I find that I can put Luke right in an opponents face with Marksman active and they will often choose to shoot at the other ships in my squadron at range 2 rather than shoot at Luke knowing he is hard to hit, has an extra shield, and his shields will recharge. An X-Wing hitting with 4 dice and Marksman can cause a ton of damage even without Wedge at the helm, and if I managed to get a Target Lock the turn before he is pretty lethal.

A nice "bonus" about setting Luke up this way is that if you find yourself in a position where you are just trying to keep Luke alive in order to eke out a marginal win, he is still a very tough ship to kill.

That's an interesting idea. I like it! I might try it out.