let's tackle this one by one.
What kind of Mac do you have (like Mac mini (Mid 2011) from the About my Mac menu)?
Is Logic really crashing and freezing? It shouldn't do that. What I get often is the Overload message.
Could you maybe attach one or more screen shots of the mixer (at least the left side and the right side), of a song that overloads, so we can see how you use your plugins, which ones you use (important!) and how you use your busses at the moment?
About side chaining:
Unfortunately the term is used in two different ways, sometimes called internal and external side chaining.
Internal just means, that you have some sort of high and low pass filter in the plugin that is used to narrow the sound of the signal the plugin should react to.
Let's use Logic's Noise Gate to explain this:
Let's say you have a kick and want to get rid of the snare bleed, so you'll use a noise gate. Unfortunately the snare bleed is so loud that it triggers the gate even before some of the softer kick hits.
You now use the right side of the plugin (the internal side chain), switch it on and then click on Monitor. You then use the filters, so you mainly hear the kick and not the snare. The gate will listen to that signal to open (or close) but it will open or close the original sound (if you didn't forget to switch of the monitor again ;-).
External side chaining is almost the same except that the gate (in this case) listens to a signal from a different track (or buss) to determine if it's going to open or not.
On the top right of all the plugins that are capable of side chaining you will find "Side Chain" and a menu with all the tracks and busses it can listen to.
We're still on the kick track but now you told it to listen to the snare track. You use the filter (with monitor) so the plugin "hears" mainly the snare sound.
Now the kick track would only be audible when the snare hits. You could then set the Noise Gate to Ducker so it would attenuate the kick track when the snare hits.
A typical side chaining trick is to lower the volume of a bass the moment the kick hits. It's usually done with a compressor on the bass track that listens (via side chaining) to the kick track. After tuning the compressor it will compress the bass every time it hears a kick.
Hope that helped.
About the busses: My Logic template with Logic plugins only is somewhere in the forum (I can't remember where I put it). It will show you how I used busses (although I have a different setup now).