Is there a way to get a count of transactions, by account, before I convert from 2007?

I can't think of any way to do this in Quicken 2007; perhaps one of the other Quicken Mac veterans will jump in here with a solution.

I will note that the log file generated by the Quicken Mac importer will give you a very detailed report about what it imported, including a count of the number of transactions in each account, and if there was anything it was unable to import.

In my case, there were a number of errors with one account from a decade earlier, and I was aware for years that Quicken 2007 had had a problem and mangled some data in this account and broken many of the transfers into and out of the account. It was fortunately a less important account (my wife's petty cash), and with the information in the log report, I was able to decide it was (a) too much to go back to try to edit all the damaged transactions in Quicken 2007 to fix them, (b) too old to be of consequence to me, and (c) that I'd ignore the errors and move forward.  If you're lucky, you won't have any such errors, but if you do, the log report can give you a good idea of the scope of the issue, if not clear-cut answers about what went wrong sometime in the past with Quicken 2007's sometimes-quirky database.

If you're able to run Quicken 2007 and modern Quicken Mac at the same time -- on the same or different Macs -- then you can methodically compare account balances and investment holdings between the two programs to see if you have any discrepancies which need to be investigated or tweaked. (A "tweak" might be something in an investment account which, due to rounding, shows a cash balance of a few cents, or a security you sold which Quicken thinks you still have 0.000001 share remaining.)

My one strong suggestion for trying to position yourself for a clean import of data is to launch Quicken 2007, and rebuild its index files: Command-Option-B. This can cure minor inconsistencies in the database which could cause problems in the importer.