I must agree with the majority of the other posts.
Having been Master on ships and both short haul and long haul on jets I gave up flying and went back to what I felt was a better career with better prospects.
The comments about not getting a look in if you go modular are nonsense. I found this to be no hinderance and your maritime qualifications and experience will be looked upon much more favourably than the average applicant.
Regarding salary, at the upper levels you could take home upwards of £120,000 with a ship's command and keep in mind that with Seafarer's Earnings Deduction that no tax or NI is due if you spend over 183 days outside the UK so every penny goes in your pocket. As previous posts state this would be possible with only working 6 months a year and you can learn to fly to whatever qualification you wish during leave and time at home giving you the option to apply to airlines at a later date if that's what you want to do.
Good luck whatever choice you make.