Selling Xbox what do I do

I purchased xbox one x forza 4 weeks ago direct from microsoft and also an extra wireless controller but due to cirstances behond my control used it a few times,but not even registered the free xbox live month free, i need to sell it.

two questions

first what would be a fair price as now there approx £400 new for both items.The consol is as new with box etc.

Second .Would i have to reset the consol but the new person would loose forza and the other digital games i have installed.or is there another safe way of selling it leaving the games including a few digital ones i have purchsed.

thanks in advance

:)