Stamp duty first time buyer renting after 6 months

I’m looking to buy my first house, but I’m only planning on living in it for 6 months or so before going cycle touring next summer (covide dependant..!). I’d like to rent it out for 6-12 months after that, then move back in.

My questions are:

1. Would I have to back pay the first time buyer stamp duty exemption
2. How easy would it be to change my mortgage to a buy to let after six months

Any help is greatly appreciated, I’ve searched online and can’t find any information about this specific situation.

Edit: This is for a property in England (sheffield) the transaction would not be completed before March

Thanks,
Alex