You must knead the dough until it becomes elastic, otherwise it won't prove and it will not bake in the middle.
Wrapping the dough, or covering it whilst proving, will prevent a skin from developing.
Prove until it has doubled in size and feels soft and springy when you poke it.
Metric kitchen scales are an inexpensive yet invaluable gadget to enable accurate measurement of ingredients. Store them upright in a cupboard or over your worktop and they'll only take up a tiny bit of space. Click
HERE for the ones I use (UK Link). For U.S. option click
HERE.