Hi Brian, Yes by all means use the membrane. However be carefull on what kind of mulch you decide to use. (i) bark, this is a great mulch but you should not use with a membrane. The reason for this is that bark mulch rots and will break down to form a kind of compost. This will only provide a growing medium suitible for weeds. Bark should be allowed to rot into the soil. It will than need replacing after a couple of years. (2) Stone chips. This form of mulch is permanent. It cannot rot and it will not diminish over time. You will however have to use a membrane as it is important to keep the stone separated fro the soil.
Also if are not a gardner, keep away from seed, as it requires some skill and space to produce and harden of the stock. Much better to buy trays of bedding plants. There is a limited variety available at the moment, but this will increase greatly from middle of May onwards. Also look into buying some alpine plants as they low growing, free flowering and easy to grow.