I'll look in regularly to see how you're doing.
To start with stick to the bookies that offer a free bet rather than a refund. The refund is a little more complicated to get your head around but once you've done a few SNR free bets it's much simpler to do the refund bets.
Always check bookies terms for minimum odds. The lower the odds you can find for your qualifier that meet the minimum criteria, the lower your liability and therefore exposure.
For SNR free bets odds around 7 need to be close, so 7/7.2 or better. Look to return at least 80% of the value of the free bet. As the odds get higher you can get better value even with a wider margin, so 20/22 would payback marginally more than 7/7 BUT your risk becomes much greater. As you become more experienced you'll find 80% easy and 90% should become your target.
Keep good records! Being an accountant I'm sure you don't need telling how to set up a spreadsheet
I currently have a float over £30K and within a minute I can tell you where all that money is to the penny.
Finally and most importantly ENJOY IT. If I feel a little sluggish or find it's becoming a grind I don't even look at my spreadsheet for a couple of days. Then when I come back to it I'm usually raring to go.