...with a neutral and evil party.

How much will this hurt me, assuming I try to roleplay each encounter?
(I've been through the game before, so any spoilers are not an issue.)

It won't, as long as you don't piss off and kill any vital characters (e.g. anyone in Easthaven or Kuldahar, and anyone that has an unfulfilled quest).

I'm <a href=http://www.ironworksforum.com/ubb/noncgi/ultimatebb.php?ubb=get_topic;f=3;t=003471>playing</a> a bit evillish right now. There isn't really as much room for evil roleplaying as in BG, but it's still possible. For example, you can choose the more evil dialogue options. Some quests (Aquarium comes to mind) have also evil option.

Just remeber:

1)If youre playing a ranger he can become fallen. A paladin too, but then I'm assuming youre not playing a paladin.
2)Don't ever make any of the townspeople red (hostile). Be carfeul of this. For example one dialogue option with the kid who greets you at Kuldahar (Nate) can make him go red. And soon everyone else will follow. If you see anyone become red, don't take chances. Reload.

Good only items are one reason not to go too bad:
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Blessed Helm of Lathander [+2 helm and spells]
Shimmering Sash [constant Blur]

And cleric spells are another:
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Heal
Greater Shield of Lathander
Holy Word
Resurrection

The game is really designed mostly for non-evil since most neutrals are with good intent and most hostiles are either undead or evil. They should design a game that has two paths for the evil in us...err...our characters.

I had heal on a neutral cleric (with expansion and trials of the luremaster). Raise dead seems to bring people back without losing any constitution, so I dont think the loss of resurrection is that bad. Just keep your elves out of the line of fire...

Heal:

Oops; forgot. I was experimenting with an evil cleric and he didn't have Heal. Since a druid gets it, it stands to reason a neutral cleric gets it too. Missed that in Logic 101.

That said once your bard reaches level 11, the importance of Heal is very reduced.

I dont know, the Heal spell is still pretty nice to have if your tank lost a chunk of HP and still is busy fighting. To me the bard song mainly makes lower level healing spells redundant. By the time you get Heal the bard songs 2HP/turn is moot in combat situations.