-Yes you can file GC without having H1B.
-EB3 category doesn't require any work experience as long as you have bachelor degrees. Skilled workers is different than professional workers. like chef and "mandir pujari" vs Java Developers
-You cannot show experience gained from the company that is filling your GC if the position is same or similar. There is a rule of difference. maybe 51 % but not sure the exact percentage. But for EB3 this should not come into play. It is usually for EB2 category.
-There are 3 steps in the process -
1st - PERM....basically proving that there is no american workers like you for company to fill the positio. Includes advertising..
2nd- I-140....making sure you are getting market rate wage and company has financial to do so
3rd - Change of Status ...Become GC from your current status...get work authorization card..This is where company might also ask you to put your money for expenses. This is your petition where as step 1 and 2 are company petition.
In this step, you include your family as well so that they get GC too..so if unmarried get marrid here so your spouse do not have to wait 2-3 years for her GC
Step 2 and 3 can be filed together (sometimes they put hold on this rule and has to file separately).