I haven't used the SD3 kits much, but I'm wondering if I'm missing a basic function... I've laid a Kick and Snare down (then when off to record some other parts) now I'm back and wanting to add Toms and such... all the midi information is in the SD3 folder, not in the individual track labeled Kick or Snare, and there is no Record switch on the individual track, so when I go back into record at the top of the SD3 folder anything I record overwrites... is the solution to simply change the record option to sound-on-sound, or is there some other step I'm missing? (I don't use the patterns, I prefer to play the parts with the pressure pads on my controller)

Yes, Sound on Sound record mode will create a new lane in the MIDI track that plays along with previously recorded lanes.
 
The other tracks host audio outputs from the synth, and you don't record those. When you're done recording MIDI, you can Freeze the audio tracks to render the audio to file.

I find it much easier to insert  soft synth as their own track and never put data there.
I then insert a midi track(s) that are pointed at the synth. 
That way I can insert other synths and try my midi tracks playback using different synths. 
That way I can have a different track for different drum parts. I always separate my kick as example. So I'll often have 3 tracks for my drums Kick/Snare and Toms/ Hats and cymbals and sometimes percussion too. 
I might then decide to use TTS-1 for Kick and percussion and Session Drummer for the rest.  
If I play a piano or organ I often record it using TTS-1 but will end up using True Piano's, Mr Tramp or Dim Pro. 
So having the midi data in it's dedicated track makes it way easier for me to experiment with sounds. 
I always use "Overwrite" 
If you use Sound on Sound you end up with a mess of unwanted overdubs lurking. I want them gone- deleted. 

My approach is slightly different again.
 
I use either BFD2 or BFD3 for all my drums and whichever one I choose, I start by inserting the synth and choose to enable all Mono outputs.
 
Then I will build up the kit as I want (or use a stock BFD kit which number close to 100 what with all the epxnasion packs I own).
Then it's a simple question of mapping the midi articulations to their own keys; routing the audio outs from BFD to separate audio channels in Sonar. Delete the unwanted channels and setting the Room, Overheads & Ambient channels to stereo and I'm done.
 
Then I'll build a drum map based on the key & channel assignments.
 
Patterns can then be either dropped in from the browser, recorded from a midi keyboard or edited directly in the prv/drum map.
 
Sometimes I'll just go with a BFD preset and just route the main stereo pair into Sonar and do all of the drum mixing inside BFD
 

Fantastic, answers and options, thanks! I'll try all of these.

I sometimes use multiple MIDI tracks as well for the reasons stated and others (e.g. having independent control of Velocity Offset). But I usually start with a single track having different parts in lanes. If a first take of a new part isn't good, I just Undo, and try again - so things don't usually get too messy.
 
And you can use drum maps to route different parts to different synths so it's not strictly necessary to create a separate track to do that. If you decide later that a separate track is needed, it's easy enough to Shift+drag a lane's content to a new track after the fact (holding Shift preserves start time).

How many years have we had these so called lanes and I still ignore their existence. 
I guess I'm still stuck in 8.5 world and happy. 
I guess we should be happy that Sonar gives you more than one way to work. 
 
I just loaded up some old 8.5 projects into Professional last night and other than the screen size was smaller everything was still was good to go.