A few mastering questions

So I have about 25 songs I want to record up real nice.  I exported all my midi tracks to waves, and set up a bunch of .cwp files with the wave files as Audio tracks.  I sent the audio tracks to (grouped) buses, like violins and cellos to a String Bus and trumpets and trombones to a Horn bus.  I have many other buses, like percussion and bass and pianos and so on.  Now, I want all the tracks to have the piano as the "main" instrument.  So that bus is always a bit 'louder' than the others.  But generally speaking, all the audio tracks are set at about -5.0~-6.0 on the console and then I adjust the buses to make the instruments sound right.

So, question 1:  Since I have my strings (for example) grouped in a bus, should I have the actual meters of the Audio tracks for those match?  Like, should violins and violas or snare and toms be at the exact same level of 'loudness'?  That is with the little Highest Peak number that shows up. 

Related, question 2: If I have my strings in the main song track, it gets kinda hard (and tedious) to hear the violas seperate from violans with all the others going and I'm not sure if one is getting too loud to drown the other.  So should I be mixing/mastering similar instruments first?  In like a template project and then import the mixed wave?  And if I do that, do I want to 'Master" first or the mixed audio track?  Or master both?

With my Mastering effects, I've been using both the default LP64 multiband and izotopes.  I got a good sound going, but it's coming a little tinny on the bass guitar, even with some bass boosts.  So where exactly should I be throwing those effects? On the audio tracks, buses, or master bus?  And if it's still tinny, how can I avoid that kind of sound?  I'm sure I have to move the eq bands, but to be honest, I'm not quite sure what effects it has and experimentation will take a really long time so I hoppe someone can give a few points.

Thank you for your time.

piira, everything you've described so far refers to what you should be trying to achieve in your MIX - NOT mastering.

Completely forget about LP64, Izotopes etc. You need to get you MIX sounding as good as you possibly can before you even THINK about "mastering" - a rather fluid term in this day and age in any case.

Read up on the subject - it's HUGE!!!!!!

Arm yourself with a couple of books (minimum) and get to know them like your best friends.

Thank you guys.

It seems that what I need to do I called mastering, and you called mixing, so I guess I was wrong on the word.  But what I think you all are saying is not to add any effects in to the mix this round.

What I should be doing now is taking all the tracks for each song and getting them into one main wav file so that each instrument can be heard at an appropriate (but not overpowered) volume and then use that main wav to add effects?  Am I understanding your suggestions right?

at one point you have and will add a compressor to your master-buss.
There are some people recommendig placing the compressor as soon as possible to the mix.. meaning, it's the 1st thing you do.. you mix into the compressor! it makes more sense to me, but everyone has his own style..
I think you are kind of overdoing it with those separate mixdowns.. is there any benefit in bouncing down the midis to wave, and those buss & main-wav files ? You should be doing great without those mixdowns!
When I do the final "polishing" then I also sometimes notice that the kick or/and bass-guitar loses dynamics/punch.. what I then do is: I insert another "masterbuss", that one is the last in my chain and only has a brickwall-limiter and spectrum analyzer. (I have another "mastering-in-buss with all the fancy stuff like compressors, eqs, tape-sim, whatever,.. right before it)
Then I send those instruments(bass/kick) from within their individual tracks to that new buss(using "sends"!).. so it's quite similar to parallel compression,.. giving me more control over individual instruments instead of squashing them all on the master-buss. (well, actually I squash them all but I feed the masterbuss with a "clean"/uncompressed signal of the tracks)
that might also work with your piano as your main instrument!