Hey Nj brother! :)
Let me try and help you out here. Ok, here's the deal with busses...
The reason to use them is to send multiple instruments to one fader for control. Drum kits have several instruments...once you get your drum mix the way you want it, you send it to a drum bus. This way, that fader will control the entire kit.
Synths: You can send them all to a bus if you wish...there are no rules. However, I probably wouldn't want a piano sent to a synth bus. Anything that is a single instrument like bass....doesn't need a special bus in my opinion.
As for the reverb sends you mention, this is how you do it. Set up your bus, name it verb, put the verb in that you want to use, and then turn the effect on the verb to 100% wet. Take all the dry signal out. Say you use a Sonitus verb. Dry in the verb all the way out, verb setting at 0 or higher if you need it. Leave the bus fader alone for now.
Go to the tracks where you want this verb to be on, right click and insert a send and look for the "verb bus" to show up. Select it and it will be on that track. Now, when that send is created, the send level on the track will be set to 0dB. This will be way too effected. Turn it all the way down and increase to taste. Do the same thing to all your other tracks that you want this verb on. Leave the synth track outputs set for the synth bus. What we are doing with the verb is a send. Though it is a bus, it's not an instrument bus. This is an effect bus. When you send your instruments to a bus, that is an instrument bus, understand?
The differences are: An effects send is a bus you create with an effect on it. Your tracks are NOT routed to it...IT is routed to your tracks using the insert send function by right clicking on the track and selecting the bus of your choice. You then control how much effect you want to be heard using the send level control that will appear after you have inserted the send on the track.
An instrument bus has an output selected on the track that is sent to an instrument bus. Your tracks are routed to the bus, the bus is not routed to THEM. Understand now?
You should not have any level issues like you mentioned. The only time levels will come into play is if you are not using the effect in a send bus at 100% wet. Meaning, if you have dry present in the plug, when you turn up the send level on your track, you will gain volume more than you will hear effect coming through. This is why I made you turn the dry all the way off and make the wet 100% wet. This will give you effect, not a volume increase. Get it now? :) Best of luck and I hope this helps.
-Danny