Hello Bro's

Nice Day for you

now i have fedora server in head office and access to it from other branches by remote access dyndns 

I want apply ERP in my company I found two ERP (NEXT ERP and odoo) it's build by python .

So

I have 270 employee's want access to this ERP I wanna implement odoo 8 or 9 but i afraid in future odoo tell me must pay to use system 

I install it in my local server and maybe in future create custom module for it 

and I'm not understand license of odoo enough( what,when is free and paid   )

please can you explain that with some details 
Thanks Bro's