Attorney question re: accident

My oldest son (age 24, lives on his own but is on my wife's health insurance) was hit by a car on his motorcycle. Other driver at fault according to officer on the scene. He was shaken up and sore at the time, but it worsened during the night and his shoulder is popping out when he raises his arms. Went to Urgent Care, diagnosed as torn rotator cuff and referred to ER, who confirmed as well that shoulder was dislocated (and reduced), torn rotator cuff. Referred to Orthopedist - said likely that they will order MRI, then probably attempt PT first, then possible surgery. Sent him home in a sling. He just got hired at a new job last week. No means of transportation right now, and will likely sell bike and try to buy a car once bike is fixed (not too keen on riding bikes on the street now, obviously).
I'm aware that La. only requires $15K of liability and don't know the other driver's coverage limits yet. My son does have uninsured motorist, though I don't know if this also provides "underinsured" drivers. Not looking to take the other guy to the bank, but obviously want to recoup loss of bike value (since once fixed it now has a wreck history which depreciates value further), costs of temporary transportation, possible loss of income (if not loss of job completely), medical bills, surgery bills, etc.
My big question is this: at what point do I make the decision whether or not to retain an attorney? I've never been through anything like this. When he contacts his insurance agent, will they handle most of this with the other guy's insurance and will they attempt some type of settlement? If the guy's coverage limits cover everything, they might not necessarily cover everything after the attorney take his cut (if UM doesn't also cover underinsured, which I don't know the answer to). Should he retain an attorney now, or wait a couple weeks and see how things play out between the insurance companies? Will hiring an attorney slow down or speed up the process - his immediate concerns include obtaining transportation and paying medical bills, neither of which he has money for.
Any insight is appreciated.