My tips would be-
1) learn to do as much as you can for yourself, such as welding, lathe-work, spraying, wheel-building and mag rewinding. Saves time and a ship-load of money, plus you can smugly say to people "yep, did it all myself..."
Paying a pro really hits the budget.
2) Don't pay over the odds for the next project. The last Vinnie out of Stevenage may well sell for a £quarter of a million, but that doesn't make a bent rusty frame + half an engine worth £15000 of anyone's money.
3) The pile of bits in the corner may be a "complete bike" according to the seller, but reality (and hard-learned experience) says it's just a pile of spare parts, some u/s, some duplicates, some unrelated, so unless you really love an expensive challenge, this isn't the best way to buy.
4) Try and get the most complete bike you can. Tanks etc are obvious when missing, but all the little brackets, levers and bits can be pains in the proverbial to either make or buy.
5) The sight of crispy tenners softens most hard-hearted sellers.....