Wealth-by-level for level 4 is 6,000gp, so you could just go by the GM items and PCs that are built should spend no more than 25% of their wealth on weapons, 25% on armor and protective devices, 25% on other magic items, 15% on disposable items like potions, scrolls, and wands, and 10% on ordinary gear and coins.
Let them kit themselves out, and bam, issue solved.
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I'd give them a couple of +1 items each, a few potions, a couple of scrolls. Personally, I think it would be better to introduce them gradually through play - the next few treasure hoards they find can be a little more magic heavy than usual, maybe the next villain can be a powerful character, armed with a few magical items they can take once they defeat him.
I usually like to allow the players to buy their own gear. Give them the GM Guide with all the magic items and let them go wild.
But Steve Geddes also have the right of it. It sounds like your group would be better off if you introduced the items slowly. It will make the magic items feel a lot more special to them.
Figure out how much gold each character has, this includes unspent coins and the value of their gear. Then make a list for each character of items you think they would like, the two lists should add up to around 6000 gp. Then over the next few sessions sprinkle these items into the treasure they find.
Tell us what the characters are and we can probably provide some better suggestions.