So using the Pathfinder race builder I built a race that's supposed to function as a sort of police force to a huge magical city, i limited the race to 20 rp.

Witch Hunter
Medium aberration half construct
+2 Str +2 Int -4 Cha
20ft land speed, not slowed by encumberance or armor
Natural armor +2
Emotionless (take a -4 to sense motive)
Constructed (treated as both aberration and construct, +4 vs mind effects, poison, paralysis, stun, immunity to disease, fatigue, exhaustion, sleep, and moral effects)
Multiarmed (the race possesses 4 arms)
Weapon familiarity: sawtooth sabre, falchion
Negative energy affinity (healed by negative energy, hurt by positive)
Darkvivion 60 ft
Does not need to eat sleep or breath

The race is a slug-like creature that gets summoned by the wizards of Ral'dar, the largest magic city in the world. They cannot survive in the world normally, so the wizards crafted them completely enclosed construct shells. They can completely control their shell. The race feeds off of ambient magic energy.

So the race is known by 3 names, Xilithrae is their true name. Guardian is what they are called by the government and normal people. And the last name is Witch Hunter, a name given to them by the outlaws and more xenophobic people in Ral'dar. The race doesn't seem to care about being called witch hunters, and will often refer to themselves as any of the three, sometimes all three in the same conversation.

Now every Witch Hunter must serve the city for no less than 10 years to "work off" the cost if their shell. After the 10 years they are given the choice of continuing serving the city or become free. Serving the city comes with perks, like unlimited access to the magic energy they feed off of, as well as the power of being a city guardian, in the effects of the half iron golem template (from errataed 3.5 MM2) without the negatives to mental stats. The Limbjack template from the Pathfinder advanced bestiary as if all limbs were replaced, 10 construct HD, and detect magic, identify, and antimagic field as at will abilities.

Now one of the things I've been wondering is what kind of CR would that be.

Also their lifespans are strange, while serving the city with the unlimited access to the magic energy, they don't have an observable lifespan. Without the unlimited access they have a lifespan of less than 200 years. Serving the city or finding another unlimited access halts the lifespan but doesn't reset it.

Are there any tweaks you guys would recommend? Would any of you play as one? Mostly I'm wondering if I made a decent race before actually implementing it into my world?

Little info on Ral'dar:
The city of Ral'dar is the largest magic city in the world, it is built on a convergence point of the magic leylines, as well as the leylines ruptured out of the surface in the form of a giant crystal. The surrounding area is a barren desert known as the Burning Desert as parts of it are actually on fire.