Answer 1

One possible solution would involve leveraging the OOTB Approval Workflow combined with a custom Event Handler.

The reason for this is, as far as I know it's not possible to make it so that a user can only edit certain fields as permissions  cannot be assigned on the column level.  However, with the Event Handler, we can catch the event as soon as the user tries to make changes to an item and if the change is illegal, we can block it.  Therefore, we can control illegal changes in this manner.

It seems as the rest of your functionality is exactly what the OOTB Approval Workflow is for except for the field changes which can be coded against by using a custom Event Handler.

Answer 2

Hello,

For Step 2  - column permissions doesn't exist in regular SharePoint settings. To do that you have several options:

1.     Use conditional formatting with SPD. there's a great post how to do that - http://www.sharepoint911.com/blogs/laura/Lists/Posts/Post.aspx?List=676af157%2D7d96%2D4e15%2Da987%2D54b8a3e4d948&ID=3

2.     Use InfoPath by customize the list form.  But This requires SP2010,SP2007 Enterprise and if you have WSS or SharePoint Foundations - it will not suffice.

3.     You can use SharePoint Add-on to accomplish that. my recommendation is for Smart List Light. Its free and it will do the job. there are many 3rd party solutions that doing the same, just Google it.
Check it out at - http://www.infowisesolutions.com/product.aspx?id=SmartListLite

Ethan

Infowise