I'd recommend against allowing large sized PCs the use of large weapons. The reason is that it's a potent feature that scales with the number of weapon dice powers grant. One possible solution is to remove weapon damage scaling based on size entirely. If you feel that large size merits increased damage, you could grant the race a flat damage bonus (+1 or +2) as a racial feature.
I think reach could be fine even as a persistent racial feature. Threatening reach is, of course, another matter entirely. I could see threatening reach as a racial encounter though.
Large size PCs do have a few other issues you need to be aware of as well.
Close bursts are larger (because the origin space is larger). One solution is to require large PCs to select one of their squares as the origin square, but in this case their close bursts are effectively smaller than those of a medium PC. Another approach would be to allow them to choose an equivalent number of adjacent squares to what a medium PC would get (8 in the case of a close burst 1), though I could imagine that slowing down the turn.
Squeezing might also be more of an issue for large PCs, though that mainly depends on the DM.