If you are set on a new lens have a look at
http://www.warehouseexpress.com/buy-sigma-17-70mm-f2-8-4-dc-macro-os-hsm-lens-sony-fit/p1518709
Also if you have not already familiarise yourself with HDR (High Dynamic Range) mode that your sony has. This is a fantastic feature and could give you some superb shots.
More and much more important though is to work out light. How you manage light is how you set yourself apart from the amateurs. You would be well advised, if you have not already is to try to find out if there is a local wedding happening and go and watch the pro at work. Find out if there is a wedding at your venue before yours and go and watch that.
You might arrange to take your couple along to the venue before the event and do a bit of practising or if they are not up for that take another couple along. Work out what you will do on the day.
One of the big advantages of experience is that most things you come across you have seen before. At last weeks registry office wedding the wedding before was coming out as my wedding arrived. My bride was in a vintage american chevvy that looked fantastic, the bride did too and I think suddenly the other bride became jealous. She decided to take route on the steps to the entrance and get all her mates to take photographs. I walked over and offered advice. I said they might be better off walking around the corner to the front of the town hall, thats where all us pros took our brides - they did not have a pro

'

'( for them


). I said they would not then be looking straight into the sun and squinting and they would have the fantastic pillars behind them. After a few seconds they decided to take my advice and moved off. I had waved my brides car to a nearby pull in and so then waved them back over.
I mentioned this to the bride and groom when I took their photographs around and the bride said she was totally unaware of anything which is what I wanted to her to say. The above has nothing to do with actually taking wedding photographs but if I had not handled it it would have effected all the arrival photographs.
Setting out on doing your first wedding you need to spend some time at the venue thinking of all potential problems and have contingency plans for them.
Totally out of coincidence after the wedding my wife and daughter met me and we went to a local chinese buffet down on the beachfor lunch. The couple from the wedding before were there with their guests. They came over and thanked me for the advice. Now twenty years ago I would have had them out on the beach to take some shots for them but I must be getting old as I went back to my noodles


stew