I need to get an annual travlecard Zones 1-4.

I have heard that if you buy it from a Rail station you can get a discount
the following year, is that true ?

Can I get one from a rail station just for Zones 1-4 ?

Can I get it put on my Oyster ?

My company offers interest free season ticket loan, do most rail companies
accept these ?

My closest station is Charing Cross, would they be able to help ?

Many thanks for your replies.