Service upgrade / code compliance
Please, get a BIG panel.

The #1 panel issue we here is "my panel is full".  This is an absurd problem to have given how panels are priced. The incremental cost for more spaces is a buck or two per space.  So max this out. 

Get a 42-space panel.  No compromises.

That is the minimum sensible size for a modern home.  This panel will assure you never have the "my panel is full" problem - which the next size down, a 30-space, can't promise.  Even if you're at 8 spaces now and 18 seems huge, trust us.  Get a 40/42.  

We mean spaces, not circuits.  The "circuits" number is completely useless because it relies on "double-stuff" breakers, and those are not available in GFCI/AFCI (big problem!) 

If physical dimensions are a factor, look at Square D "QO" or Eaton "CH" which have more compact breakers, and put 40 spaces where others put 30. This is not double-stuffing.  

Better ways to get a 150A main breaker

150A/42-space panels are rare enough to not bother looking for them. You're better off with a breaker panel  "Value Pack" that tosses in some bonus breakers.  

If you have a main breaker upstream (e.g. at the meter) then the new panel doesn't even need one.  If this will be the main breaker, you have two ways to get a 150A panel in many panels: 


If it has a main breaker larger than 150A, you can swap it out.  
If you buy a convertible main-lug panel (which has space for a main breaker) then obviously you can select 150A. 


Store advice

Never talk to a Home Depot, Lowes, Menards etc. employee again. Their advice is worse than useless.  Electrical supply house managers tell me they visit those stores and hire away anyone good. 

GFCI/AFCI breakers

If all you're doing is replacing the panel, there's no requirement to fit all AFCI/GFCI breakers.  This is because of the concept of grandfathering.  You would be required to do that if you remodeled or significantly altered the circuit, and that is irrelevant to whether you upgraded the panel.  Your ability to do this in the future is one reason you need a big panel.  They don't make double-stuff AFCI/GFCI, and they never will.