I have created a custom module that adds a field show_separate_invoice to the ir.config.settings. Now how to check the condition if show_separate_invoice is checked or not? And if checked, how to  get the custom field journal_to_invoice value from another module(sale.order)

class CustomSettings(models.TransientModel): 
 _inherit = 'sale.config.settings'
 show_separate_invoice = fields.Boolean('separate_invoice')
 journal_to_invoice = fields.Many2one('account.journal', string='journal')
 
 @api.model
 def get_default_show_separate_invoice(self, fields):
 irconfigparam = self.env['ir.config_parameter']
 return{
         'show_separate_invoice': irconfigparam.get_param('show_separate_invoice', False)
 }
 
 @api.multi
 def set_default_show_separate_invoice(self):
 self.ensure_one()
 irconfigparam = self.env['ir.config_parameter']
 irconfigparam.set_param('show_separate_invoice', self.show_separate_invoice)
 
 @api.multi
 def set_default_journal_to_invoice(self):
 return self.env['ir.values'].sudo().set_default('sale.config.settings', 'journal_to_invoice', self.journal_to_invoice.id)