im pretty nnew to this too but i can answer most of your questions.
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define: fluff, fluffiness etc
fluff is the background story to the whole 40k universe. its all the fictional stories that make it much more interesting than people fighting.
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any good mail order/trading sites?....what is usual "rate " on trades/ buying used/primed models (ie 50% of new cost?)
the best retailer i found so far is
www.wargamesworksho p.com which has something like 20% discounts on most things. if you do look at them, check out their army deals, especially the "huge army deals", they have huge discounts.
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how much dough should i expect to spend(stupid question huh, i know the answer is Too much!)
for a 1k-1,5k point force probably 200-300 dollars depending on race, how many models, and what points you are looking at. this is just what i estimate to be, it could be different. you also need to buy paints and glue and whatnot, but that shouldnt be more than 30 bucks to get you started. you will undoubtedly want more units and probably more armies later, though, but thats for draining later paychecks :-)
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please explain cross fire rule(rb is shady)
crossfire is rule that says 'when a unit is forced to retreat into an enemy unit is is completely destoyed.' this is v3 rules and simplified, but the basic idea. when units fight in close combat, there is ussually a winner, and the loser has to retreat. if the loser retreats into an enemy unit they are completely destroyed, like being cut down in the crossfire. no where to hide. hope that nswers the question. if not, im sure someone else knows better than me.
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anyone near detroit who wants to whip up on a noob?
i live near cleveland, so i cant help you here, sorry :-)
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so, there you go. have fun!