Cache is not required for Share. Specifying a "upload" folder is required for Share's startup checks, but you are not required to have anything in the folder. Share will still function just fine without any uploads. PerfectDark, the new P2P network intended to eventually replace Share, requires a 40GB cache, and downloads will be halted before the first 4GB and throttled while cache builds from 4→40GB.
How long Share takes to find a trigger depends on how old the file is and the cluster keywords you use. If the file is very old, then it may be difficult for Share to find peers that are still uploading the file. You should also check that your cluster keywords describe (thematically) the type of file you're trying to download. Share will search for the trigger among nodes that share the same keywords.
ID/trip is not necessary. But if you are downloading files that frequently have "fake" content, you may find it beneficial to filter your triggers for files uploaded by users you trust, hence the ID/trip field.
You don't need to refresh nodes frequently. Share will automatically get new nodes as it connects to the network (similar to Peer Exchange in bittorrent). I load new node lists about once a month. If you haven't used Share in a long time you may find it helpful to manually update your node list.