Hi ProKen, I endorse what others say. There are two issues, recovery from the immediate trauma of surgery and the longer-term recovery from the damage to the urinary system.
Removing the prostate involves cutting through the abdominal wall - which consists of the muscles you use to brace yourself when doing a golf stroke or gardening. The last thing you want is for those muscles to be pulling on the wound before it is fully recovered. So best to avoid too much effort for a couple of months, and be cautious for at least a couple more months after that.
The other thing which you will most likely find becomes an obsession is urinary control. The prostate sits immediately below the bladder, with an important sphincter right where the two meet. Removing the prostate is likely to damage the sphincter to a greater or lesser extent - every man is different and no one can tell your risk in advance. For the first couple of weeks after surgery you will have a catheter emptying your urine anyway, but after that is removed you will most likely find that your sphincter functions very poorly (a few lucky men do recover continence quickly). You will have a life dominated by pads and proximity to a toilet initially, but control will slowly increase though with a risk of accidents.
So, in terms of your "favourite things", you will need to follow your body as things improve. Both golf and gardening involve those abdominal muscles, which increase the pressure inside the abdomen and tend to push down on the bladder and put bigger demands on the just-recovered sphincter. You will find it soon gets tired and start to leak! Start by doing a little and then working up as you improve; aiming for a full round of golf or an afternoon digging straight away would be very dispiriting.
The alcohol in beer - like caffeine - is a diuretic, and increases urine flow. Again putting more demand on the sphincter. Early on you will only be able to have a little alcohol before it becomes a problem, but then more and more with time as long as your recognise your post-prostatectomy body has a limit. I ended up fine with a certain amount of drink (say, 3 pints of beer, or a bit more than half a bottle of wine) and indeed am sitting at home with a beer as I write this. But you can still run into problems - as Francij relates parties are risky situations where you easily lose count of drinks, tend to be standing and possibly dancing which involve abdominal pressure in the way sitting (which is what I am doing now) doesn't, and lead to you leaking. Once you start to leak you will continue, it takes time for your sphincter to strengthen up again.
Good luck! You are not alone, you are starting on something which many of us here have been through and been able to deal with in our lives. If you have questions, just ask.