I will then earn an absolute maximum of 2500 duty hours per year at £2.40 minus tax (63% Notional 87p tax free) works out at £1.92 after tax equalling a max of £4800 PA = £400 pcm
You're not anything you say you are...
We'll gloss over the dubious tax rate. (you've 100% taxed allowances at a rate of 20%)
As you would know if you really were MF crew you would be paid the hourly rate from check in to check out not just duty hours. So there is no "absolute maximum" indeed you could check in on 1st Jan and check out on 31st dec and earn 8760 duty hours. If you're expecting to be at work or on nightstops for only 28% of the year you're going to be disappointed.
And why do you need a full month travelcard? You wont be doing more than 10 return trips a month at £1.30-£2.70 per single journey. So even if every journey is in peak hours (highly unlikely) thats only £54.
And you would have full knowledge of the performance pay scheme too. But you seem to have missed that out.