What you should know:
a) Whispering Cairn is one of the best low level modules ever written.
b) It's not a cake walk. Whispering Cairn in particular will challenge all of a RPer's skills from tactical combat to good role playing. Despite being a low level module, this is not a module for the faint of heart, foolhardy, and inexperienced. You are going to need wits, deductive ability, dungeoneering and a well crafted party that works together and players that keep thier heads if you want to survive. It's better that they go in with the idea that this is 'Tomb of Horrors for 1st level characters' than not take it seriously enough and get whacked by an early trap.
c) The later modules vary in quality IMO. Some of them are simply (unimaginative IMO) combat slogs. Others are creative combat slogs. Expect alot of combat. Different chapters will appeal to different groups, but while none of them quite match 'Cairn's for variaty and level design there is good oppurtunity for everyone to shine - rpers, dungeon crawlers, tacticians, puzzle solvers (not enough of this later after the first module in my opinion though). A good mixed party is probably the best approach, though I'd lean toward clerics and fighters. (Rogues have comparitively little to do IMO outside the excellent first chapter and (IIRC) sixth chapter. Lots of undead, and only a couple chapters were traps matter significantly. A mage isn't needed until near the end of the path, and then oh my are you going to need one.)
d) Someone said, 'You need a cleric.' This should go without saying. The cleric is the most powerful class in 3rd edition, and the most indespensible. But, here I think you really need a cleric. No joke.
e) It's should be easy to modify to run in Eberron. Full notes for the conversion have been provided in supplements to the adventure path.
f) That said, any conversion is going to increase your work load. In my experience, a published module takes at least an hour of preparation time per 10 pages or so in order to get it and yourself really ready for play. Increase that if you are doing a conversion. The whole adventure path doesn't have to be readied ahead of time, but don't just buy the module and then sit down and think you are going to do it justice. Towns will need some fleshing out, you should prep some minor NPC's to give the place more life, you should set out a timeline, get some weather events thought out to increase the atmosphere, give some thought to the environs and the local culture, and add your own touch to the thing. Writers can't put everything that they would do into a module. You have to put back in what they had to leave out. In your case, just familiarizing yourself with the text and thinking through the ramifications of a world conversion will consume a few hours.
g) I haven't got a chance to run it, but it doesn't look that hard to run although a new DM may find the chapter revolving around the dinner party challenging. The text is exceptionally well written and usually very detailed. Just make sure you have the structure of each chapter firmly fixed in your head before trying to run it. For one thing, while there is some subtle railroading going on, you need to be able to compensate when the PC's inevitably jump off the rails and do the unexpected. The more you daydream and make notes about the setting, the less panic this will cause in you.
I suppose that's pretty basic advice and if you've done this for a while you don't need to hear it, but I like to ramble.
