The first three are easy. Go to the content manager and select the car that's causing the problems. Right click on it and select 'edit' and then select 'edit in explorer'. An icon that looks like a black hammer and wrench cross will appear. This means that the object is 'open for edit'. You can find all content that's open for editing by selecting the 'Open for Edit' tab.
When you select 'edit in explorer', a file will pop up. This contains all the things needed in order for an object to be available for use. Select 'config.txt'. When you open the 'configuration file', better known as 'config file', scroll through it and find the Tags that are causing the problem. Simply select them and delete them. Save the changes to the config file and then exit out of the config file and the file that popped up. Left click on the object, select 'edit' and then select 'commit'. This will solve your problems.
P.S. I selected 'SP Daylight Chair car', made by magicland with the kuid <kuid:58843:107>, right clicked and selected 'View Errors and Warnings', and the last two errors you listed showed up as warnings instead of errors. I don't think I mentioned this, but when you select 'View Errors and Warnings', at the top it'll say 'Validating', then changes to 'x errors and x warnings' (I'm using 'x' to represent a number). Remember: Errors show up as a red circle with a white 'x' in it, while warnings show up as a yellow triangle with a black '!' in it.
Actually these errors are easy to fix.
As you said open up the config.txt file using the method above.
Find this line and put in a space or spaces after the 0 and after the 2
Error: The Tag '0-<kuid:58843:50020>' .....
0 <kuid:58843:50020>
Tag '2-<kuid:-10:149>
2 <kuid:-10:149>
Like this.
John