We're currently using an old version of Salesforce which was specifically developed by "Give Clarity" called "Supporter 360". We also have an instance of NPSP which was initially set up by a predecessor who started creating fields ready to migrate. There would be around 5000 contacts to migrate, but also organisations, batches, campaigns, projects, reports, regular giving. We are a very small charity without much of a budget- I'm already working on identifying unnecessary fields etc. and am willing to put in the time, but only have basic Salesforce skills.