Never mind you about Salesforce, just taking on all the flavor-of-the-month open source ERP/CRM service providers is going to be a mess. If you're already looking for Salesforce then you are not listening for anything else, anyhow. Typical open source ERP/CRM service providers are not sustainable models of business... it is more akin to multi-level marketing schemes.
This is especially as ERP/CRM systems are not packaged software you can buy off a shelf. They are heavily customized applications.
If you're a small business, sure you can start with one of the many programs out there. But as soon as you do, you'll find you'll need to add to it because they will never cover every case - your company will do something unique, and that has to be added. Then you let it become a bit more - because if it can do one thing, just add a bit more to it so another part of your business can be handled by it. And eventually it becomes a heavily customized application running all sorts of aspects of your business.
If you're already a big company, then you're hosed because your ERP/CRM system would've developed organically the same way and now you want to migrate to a new system, which requires retraining people on the new system, but even more, requires data migration as well as getting all aspects of the old system into the new. There are bound to be odd niche use cases used by someone to run off a report or other thing.
It starts off as a simple database of customers and orders and manages leads from that. But it often grows well beyond that.
Most companies eventually build their own ERP system organically - it probably starts as a spreadsheet, then someone decides a database is better, then things are bolted on. Of course, this usually results in a horrendous unmaintainable monster within a few years.
All the CRM systems offered are just platforms for customization to get them to start application development, hopefully in a way for them to result in something that's still maintainable in the end.