Welcome to the BAA – I am sure you will enjoy your membership. I wish you success with your return to astronomy.
Glad to hear that you have an interest in variable stars – the Variable Star Section (http://www.britastro.org/vss/) is just the place to start. You are quite right that you can make a real scientific contribution in this field – the VSS has been contributing to science for 124 years! Feel free to ask any questions you might have – there are quite a few variable star observers who can help you. Are you interested in visual or CCD observing? Either way, you will have lots of targets accessible with your Celestron. You might also like to know that the Section is holding a meeting on June 21 in York – a bit of a hike for you, but worth considering.