Hello eurohelmets,
Thank you for posting your question here on the ExpressionEngine forums.
You can update ExpressionEngine from 1.6.3 to 2.4. Just follow these directions closely.
Your Add-Ons will be effected. They will need to be updated after the update. The update document has this in the header:
Third-party add-ons from version 1.x will not work with ExpressionEngine 2.x. Please contact each add-on’s author for a 2.x-compatible version before upgrading, or your site may not function properly. The installer will automatically disable all extensions as part of the upgrade process.
I hope this helps. Please let me know if you run into any problems. Be sure to back everything up before you update.
Cheers,