I think that 8 hourglass has their widest point at the hips whereas an X hourglass is wider at the top of the thigh... I could be wrong.
I think 8's can gain weight at the hip - "muffin top"/love handles" but I think other shapes also can too.
There are so many variables with body shapes and also preferences that it is hard to give advice. For me the biggest things to look for are
- length of top - not too long or not too short
- top not being too boxy (a drape works well)
- not having sleeves that end at my bust
- not wearing wide belts at the waist
- being cautious about tucking tops - it works if the fabric is drapey or fine or if the contrast is low.
- dresses are often easy