Hi there - I completed in November and did a flying visit in December to "move in". It was a hectic 3 days and that was with a full furniture package already installed!! I have 2 bed quad villa so a flat might be a bit easier but be prepared for some hard work!!
As Sping said, there will probably be an alarm already installed - you need to contact the company as soon as you arrive so they can activate it while you are still there. Louis from the alarm company will advise you about the grilles - he recommended that I change most of my ground floor ones as they come off really easily.
You don't say if you are going to rent the flat out or not - I'm renting mine and am using Citrus-Iberia.com to handle everything - they are organising my Sky package and it might be worth a look at their furniture pack too, I'm not sure how competitive they are but I really liked the local reps and they have emailed me regularly to let me know that the house is OK.
I would strongly recommend that you get the furniture and lights and white goods in before you go - a few days will not do it!!!
I didn't find a local map but we cheated and used our GPS system! There are lots of supermarkets nearby - there is a small one on site and there is a huge Carrefour on the main road into Torrevieja which you can't miss - you need to go past it and turn around at the next roundabout to get in.
We went to Ikea in Murcia for lots of stuff but it was quite hard to find - I'd suggest dowloading the directions from their website before you go if you want to visit - takes about an hour from Playa Golf. Also got my TV & DVD from Alcampo next to Ikea and I think I got a pretty good deal.
I am really delighted with my villa and hope you are happy with your flat. I've got lots of photos to download so will try to do them tonight so you can have a look before you go out.