Growing a mango tree in a medium pot, pruning?

I'm currently trying to grow a mango tree in a pot indoors, as it's too cold to put it outside and I worry the temperature change will do it harm. However I've heard you're meant to cut off the lead shoot to encourage branching? But what is the lead shoot, is that the latest shoot, or the top of the main stem?
Also, will my mango tree grow large in a medium pot, or should I pot it up into as large a pot as possible to encourage it to grow well? Thanks in advance, I'm rather new to gardening.

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