So some clarification on ADP on MSI gear. Yes some MSI gear came with software ADP, but not all of them. It was a flash code option. I have XTL2500's for SAR that have Hardware ADP/AES as once you add any other encryption you need to be hardware. When the APX series came out ADP was standard and free. That has changed to a option but still can be had. Regardless of secure type (ADP, AES, DES, DES-XL, DES-OFB) if its set for hardware with a MACE board you will need a key loader of some sort to load keys.
Also when you apply for your license you will need to determine your modulation. You can have multiple on the channel but make sure they add it to the license while applying. Adding DMR/P25 to your analog emission is what a lot do. If you know your never doing DMR then dont worry about it but again its part of your license.
I'll add DMR is a more economical digital standard for B&I stuff where as P25 is the standard in Public Safety. The reason really boils down to cost. Yes you can buy used LMR gear but if your looking at new stuff a XPR is a 1/4 of an APX.
Also if your only looking for a few portables, repeater and maybe a few mobiles talk to you local LMR dealers. Alot run a SMR system (most likely DMR) and you can rent airtime and not worry about repeater sites, maintenance etc required with your own stuff. And it allows you to dabble with a service until you decide what you want to do. When I was in the shop days I think it was $15.00 a month per radio and got alot of folks on the air over night per say.
Definately do research if this is for a business use. Sometimes a basic simplex system is all you really do need..