HI sensie! (Love the name!)
I couldnt' tell you what weight a 5'8" figure girl would come in at - it would depend alot on her build. I"m guessing prob around 130? This includes probably a bodyweight of around 140 minus 10 lb water weight after depletion. But generally you are looking at being a feminine 10-12% bf. The look usually involves a 6-pack abs, wide shoulders, nicely capped delts, long lean quads w/ a sweep, tight ass but not glute striations. LImited vascularity and again no striations.
If you are still on the primo/var cycle that will do alot to preserve your muscle, but there as you are approaching a competition date, you can probably afford to lose some muscle for a figure comp. Figure comps tend to be more about the presentation of some muscle, not all about who has the biggest muscles. I've seen plenty of girls who have really amazing quads get passed over completely because they weren't proportional, for a girl who is much smaller but more proportional.
To that point, I would also see where you are at w/ the var / primo / bulking and depending on whatever your target show date, start adjusting your diet, training & cardio to approach the look you are trying to get. Something to help guide you, esp ifyou are coming from a larger build, is to find a pro figure girl who has a similar build to you tha you would like to look like on stage.
For me, I'm coming from a BB background & need to tone down a lot of my size, particularly my back & biceps. The devolumizing process is going to take me awhile, so I"m doing a BB show as a first step to get me leaned down, but then taking 3 months to prep for a figure show this summer. My progression is to get my body to a shape like Susanne Neiderhauser (
http://members.aon.at/snieder2/news.htm) and then progress down to something like a tall Monica Brandt (can't find someone w/ the wider shoulders just yet, but that's the idea...)
Looking forrward to your pix. And yep, bodyfat is the big important number to start with!