Yes, you can use memory card in this phone.
Vivo V5s is not much heavy. Despite of having 5.5 Inch display and bigger battery, the phone weighs just about 154 grams.
Yes, Vivo V5s does have hybrid sim slot. However, phone's internal memory is 64GB and you can also expand with the help of OTG.
Yes, Vivo V5s 64GB comes with front camera LED flash.