[RPG] Are there Pathfinder rules that restrict a new PCs magic item purchases

It has to be the case that any penalties due to essence loss are applied after your Magic attribute is determined at chargen. Otherwise, by the rationale you gave above, you could purchase any amount of ware at character creation, and you would have no penalty. If you want to nitpick, gear-buying is the last leg of character creation; I don't think that matters, though. If you get ware, you will be at a penalty. There's no way around that. (Oh, unless you get the ware removed later... then there's a monstrously expensive genetech treatment to get back the lost Essence.)

As an aside, why not get a neural net for your commlink, instead of getting one implanted? That way you can use full-immersion VR, send text messages secretly, or whatever, without any augmentations.

Edit: It specifically says 1 full point of Magic or Resonance, AND the maximum for that attribute (SR4A p. 68).

Edit 2:

You must purchase awakened qualities at character creation, because magic is something that you're born with. In SM, you can purchase qualities that give you "latent" magic; but, nevertheless, your character has the potential from the time they're born, so it makes sense for them to take the loss, no matter what point in their life they get the 'ware installed

Do they have the corpses?

Do they already know where the corpses are? Do they have access to them? Are they already in someones possession?

If the party doesn't currently have the corpses but does know where they are... then it's easy: by time the new characters get to them, someone else has already looted the bodies.

If you think the party can actually get the items on the corpses, lower their starting wealth appropriately. Character wealth guidelines are guidelines, they can and should be altered as needed.

If you can't do that (because the players will be angry about it), then you'll have to alter the upcoming encounters to lower the amount of loot they get until they're back in line with where they should be.

Unintended Consequences

If you just use the wealth rules as-is but also let them get all their previous character's stuff back, you're encouraging them to change characters every time they die. Doing so gives them a major wealth boost.

There's lots of reasons you want to discourage that:

1. It encourages people to die, and punishes those who don't die by having them fall behind on the wealth curve. That makes everyone reckless.
2. It absolutely sucks for trying to tell a coherent story in a campaign when new characters are constantly coming and going.
3. It also sucks for player RP and character development, as the party is constantly changing.

I was in a game once where resurrection was strongly encouraged, because a new character would come in with HALF the wealth of the old character. Granted in the event of a total party wipe he likely wouldn't enforce that, but we wouldn't be able to get the gear back in that case either without so much work that it'd just be an adventure of its own.

If you wanted to retire a character, you would leave the party while alive (with all your gear, so the party gets no wealth boost), and your new one would come in with full equivalent value. As a result, that only happened when someone was unhappy with their character and not because the character wealth chart said they could get ahead by doing it.