If you start them in the spring when it warms up - you can use a sharp knife to split them into threes depending on the size of the Tuber of your Sweet Potato & take cuttings off the shoots that shoot up if you take away a slither of the tuber of your main tuber they will toot easily to increase your stock - a perlite 50/50 compost mix & place out of the sun they root easily - spring has to be normal not like last year's cold spring - patience is everything in propagation, & growing plants of any type plus common sense in an unheated Greenhouse -
You are doing well as the price of Sweet potato Slips is very expensive - save the ones you buy & enjoy when in the shops in season