I'd start in 1967 and march your way back. Then you really can only buy top grade coins right from the start (which is what I'd do if I had the chance to start again, would have saved me about 5 years!), you can learn grading with coins costing a few quid, make a few mistakes, only costing you a couple of quid, and move up slowly. Then on to £10 coins as you progress through G6 and G5, learning what's easy and what's trickier, throw in as many varieties as your patience can bear, so by time you're thinking about spending £100 on a coin, you've had a few hundred through your hands and you will know what you're doing a bit by then.