Unless you are counting yeast cells under a microscope, its pretty much impossible to tell a) how much yeast you are pitching b) the viability (how many cells are actually alive).
Your WL vials and WYeast smack packs are about 100billion cells and are usually pretty good for a 5-gallon batch of beer although its always good to do a starter (which increases cell count and thickens the cell walls).
Which gets to issues you might run into by over-pitching ... basically, you might get a bit of a yeasty taste if you really over-pitch, but more often the problem is that you get too dry of a beer - which may not be desired for some styles (in fact, for some styles you want to intentionally under-pitch in order to get an estery - fruity - character). This might come across as watery, or lacking in malt character.
As for your volume of yeast - its hard to tell what you have without hearing your process. The yeast should have a nice creamy white look to it. If it is granular, green, brown, peanut buttery, etc. It's likely you have quite a bit of trub still in there.
I usually boil 4 liters of water (cool it) then pour it onto my yeast cake to create a slurry ... After about 5-minutes I will pour the slurry into my 5-liter flask. After about ten minutes, I pour that into two quart jars that are a quarter full of sterile (boiled/cooled) water and shake it up. After about 15-minutes I pour the top of each quart jar into a sterile pint jar.
By the time each pint jar settles out - I have about 1/3 inch of clean creamy white yeast at the bottom of each jar ... this is about enough for a 2-liter starter for my next 5-gallon batch.
