Two of those features can be done using Google Sheets as you suggested >* Ability to have multiple team members in my company share and update my list of conta

Two of those features can be done using Google Sheets as you suggested >* Ability to have multiple team members in my company share and update my list of contacts >* Ability to group contacts by company or conference etc. so I can contact them at once. And you can possibly create API integrations between Sheets and your inbox etc using Zapier.