Darren, I believe the new threshold for Vat registration is £64k, so don't do it if it is not necessary.
You need to go on the H & M website and read up on Vat etc etc, there are different schemes and you choose the one that is suited to your business. You need to discuss this with your accountant too.
Swallowing vat for existing customers is very noble, but if you present it correctly to them, you should not have a problem. If you have a £100 customer pre vat, you get £100. Charging vat to the customer would make that price £117.50. If you don't charge it out and include the vat in the £100 price, you lose £14.90 (dependant on what scheme you go on)Multiply that out by 150 customers.... that is a big loss on your earnings.