Okay, well this is based on my laptop, which has failry low specs.
For a character, I like to stay in the ragne of about 800 (if he's just wearing basic clothing, fairly low-poly) to around 3000 (if he's wearing armor, fairly detailed). However, many more are used in most commercial games now.
For weapons, I like to stick around 300 - 1000, depending on what weapon it is and how much detail is required. Obviously, a sword or axe is probably going to have a much lower poly count than a shotgun or rifle. Once again, though, more polies are used in commercial games often, even though we have normal maps.
By "dimension in pixels suitable for the models" I'm assuming you mean the textures. I typically use 1024x1024 for characters, 512x512 for weapons, the same for furniture. Commercial games often use double that.
I hope you don't take this too seriously, as like I said I'm basing this on my laptop, which isn't very good.
Let's see how many people actually take the time to read this...
