Your view is quite frightening and with that view you are right to have doubts. Your first big shock, and as a graduate all the more so, will be IOT. Few wash out here but I am not sure you would make it. I have a nephew at Dartmouth ex-Newcastle, he does everything with a big grin on his face.
Now, drinking culture. True it happens but not as in days of yore. On operations or even routine flying the work pace limits your drinking. Heavy drinking and high tech don't mix.
I can't comment on holds, but they do present opportunities.
Now your 15-20 hours per month suggests fast jets. You may get something else. But even 15 hours a month can be 10-15 trips and one hour of flying takes many more hours preparation and debriefing. Admin happens but don't forget QRA standby, simulator sessions, operational study etc, even gym work (shock horror).
Then there are many other diversions available that demand your active choice - scuba expeditions (daughter and son in law done that), sailing, climbing, war walks, university short courses. The only limit is operational tempo and your initiative.
Disadvantages are history, positives are the future.
Multies mundane. Possibly but don't imagine a high flying civilian job won't become mundane.
Finally, unfavourable parts of the country; not many bases left so define unfavourable? Multies Wiltshire or Lincolnshire, maybe Scotland but less likely. FJ, Norfolk, Lincolnshire, Scotland.
Really it is up to you. If you think uniformity and discipline are not your things then you are right to have doubts.