Use DSTV HDMI receiver in Lagos

Hi, new comer here.

Does anyone use DSTV receiver with HDMI output? The house I am staying has an old analogue receiver that is dying anyway, so I am thinking about an upgrade. But when I went to Game in VI and a few other shops, all receivers with HDMI connection has sold out. And staff doesn't seem to understand my questions anyway.

So can anybody please tell me that

1. Whether a HD receiver with HDMI makes big difference in terms of viewing quality in Nigeria (My mates and I watch a lot football and movies, the 46 inch TV seems wasted on the old analogue receiver. We know it makes big difference in the UK)
2. How much is it?
3. Do I need to sign a new contract with SDTV to have a new receiver; or can I just buy a new one and continue to use my old receiver’s credit card sized key with a chip?
4. I know a bit about electronics, so I know that my house gets TV signal through Dual LNB (the 2 white wires) which are currently connected to my old analogue receiver. Can I connect an HDMI receiver to those wires?
5. Where can I buy a HDMI receiver?(I know if I turn up at DSTV headquarter, I can probably get one, but I am trying to find somewhere closer)

Sorry for the rather detailed questions. Any advice would be appreciated.