Hi Richard. Firstly I currently work within the Merchant Navy so can relate to your position.
You should have absolutely no problem fitting an intensive course within your assigned 2-3 month period, If you really push and have the ability it is certainly possible to complete a PPL in a 4-6 week period weather permitting of course.
To do this successfully would require you to be focussed and do some theory on a nightly basis. Alternatively you might find it much easiser to spread it over your 2-3 months depending on your circumstances.
With regard to training establishments, the advice generally is always to visit a few and see where you feel you would fit in best. I can wholeheartedly recommend the quality instruction at inverness having done my own PPL there(damn that's my anonymity blown
). Inveness also benefits from being commercial but also quiet and is perfectly placed for some excellent cross country routes.
In terms of aircraft you would have the choice between training in the PA38 Tomahawk (most common) or the PA28 Warrior. The Warrior is a four seat aircraft and is a little more expensive per hour.
I personally would opt for the Tomahawk as a trainer as it is a little more challenging and responsive, although the Warrior is more spacious and has a greater maximum take-off weight than the Tomahawk should you feel this is an issue for you.
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