New home office

Hi, I am self-employed and have some questions I was hoping I could get help with.  I recently quit my regular day job and will just be working on my self-employed/gig work/contract jobs full time (which I have been doing as a side job for years).  I converted a home office space that I didn't claim previously.

 

1.  I will have start-up costs for the home office/full-time conversion. I started setting the office up in October but didn't get it completed until February.  Do I claim that on this year's return or next?  Also, will I need to do depreciative value on my desk and laptop and how do I figure that?  And I had to have new windows put in that room, will I be able to claim those as well?  

 

2.  I imagine I will have to start paying estimated tax payments and have no idea how to do that.  Can I just log in on Turbo tax and send them?  And what percentage of my income do I need to save for that?  I should be around 30k a year.

 

3. I know I can get a deduction for the "employer" half of my tax bill, but am not sure when or where or how to claim that.  

 

4.  Also I understand I will be getting a 1099 from Paypal after this year.  But I get 1099s from each company I contract with already - how do I make sure I'm not making duplicate payments on the same income?