Well certainly surfacing around three DD's would be sure death in real life. The stock deck gun is much more strong than it should be. RFB and TM are both wonderful and you will like both. RFB is what I'm currently playing and it is terrific. TM is much more difficult than stock and you will find surfacing near a destroyer is certainly a bad idea.
You will be happy with either. May I also recommend RSRD for the realistic traffic. It makes it much less a shooting gallery and a challenge to find targets.
As far as retirement, it was modified in 1.4 at the request of many. Complete your objectives and you will keep sailing but sometimes you'll be offered a desk job and if you turn it down, you can keep sailing but lose renown.
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