First I'll take a moment to welcome you to HealingWell. We do hate to see new members, but everyone here has been down the same path.
The Gleason score is expressed as 'highest volume' + 'lower volume', so a 4+3 has more 4 than 3, and 3+4 is predominately 3, less 4. The more important number is the 4+4, which does put him in the aggressive category, and is what the doctor will treat. It looks a lot like my own scores at biopsy.
You have some time to get busy understanding PCa. I would start with one of what I consider the two best books out there, either Dr. Patrick Walsh's third edition "Surviving Prostate Cancer", or Dr. Peter Scardino's second edition "Prostate Book".
As to diagnosis, I would suggest (and his insurance company may insist) that he have a second opinion visit with another surgeon, and a consultation with a Radiation Oncologist who specializes in PCa. He may also want a second opinion of the biopsy slides. Bostwick Labs is a respected lab for PCa-related pathology & tests.
There will be more tests, primarily a CT scan and Bone scan, both of which you will likely be told are a waste of time and money by others, but it will give him a baseline, and hopefully rule out any current metastasis. The doctors will insist.
The next few days and weeks will be full of tests and near panic, but the panic is not of any value, so don't. Take the time that is needed to understand the biopsy report (get a printed copy), and get some additional opinions.
Also have a look at this thread:
Prostate Cancer: The Really Useful List made by HW people for HW people.https://www.healingwell.com/community/default.aspx?f=35&m=1717641
And, as he goes to visit doctors, have him take someone along to take notes, or better, if the doctor permits, take a recorder and tape the conversations. After time, you will be amazed what was said but missed or simply misinterpreted.
All that said, I see that 7 replies have been posted while I'm writing this one, so I may be repeating the others as well.