sewerrat is correct; I could sit here and type out what and how, but the vendors of these things practically design them for you. They will give you specs, CAD details, accurate cost (they will give you an actual quote, if you so desire), pump curves. They will also back you up on the RFI/RFC's after bid, which saves you huge. All for free.
You will have to design and cost out your own forcemain, but, again, the vendors of the grinder pumps can get you started.
Please keep in mind the person assisting you will be a sales rep (who may or may not be a licensed engineer, about 50% of the time each way). This person's job is to sell things, so your due diligence to the client will be to watch the "accessories" and "options". But, I have always gotten design help which is both accurate and correct.
Hydromatic and Goulds are two respected names, there are others also, but start with their websites for local reps. You will certainly have all the help you need by this Wednesday (it's Saturday now), if not before.
Remember: The Chinese ideogram for “crisis” is comprised of the characters for “danger” and “opportunity.”
-Steve