Let us know which ones you are considering, and I'll give you some ball-park suggestions.

Only an ounce for 3 pounds of soapis a small amount, me thinks.

The only time I have had the soap not saponify is when it went together too cool. I always heat to 110F, or just a bit hotter, then as it cools it traces in the mold.

I used to wait and worry about trace, sometimes for a long time. Sometimes it traces right away. It just depends on what is in it. The FO you use will make a big difference in trace time. I use FOs and don't add it until just before pouring into the mold.

I make large batches with about 1200-1400g of fat and I use about 15ml of FO per batch. Any less and it doesn't last in the cut and aged soap. If you want it to still smell at Christmas, you need to add a lot.

One ounce per pound of oils of most any fragrance will be enough, whether it is EO or FO.
Most FOs, I will use .75 of an ounce per pound of oils, depending on manufacturer.
EOs, I will use .3 to .5 for spices; 1.0 for citruses; .75+ for florals. Now, you can get 5x to 10x citruses and you can get away with using less.

Lavender buds may look like dead ants in the bathtub. :(

Make sure that the Vanilla FO is non discolouring.
Oddly enough, vanilla EO will turn your soap, beige to brown depending on how much you've added. Whereas, chocolate won't turn to a chocolate colour at all.

Consider using only the EO or FO for your lavender., vice both; unless, you like the combo of the scents.

Trace will depend on how much water/liquid you are using. I typically use a 30% liquid discount. I think you can do this on lye calculators on the net.But again, the more water/liquid you use, the slower trace will be (I sure hope that you are using a stick blender?).

Here's where I disagree with the advice from Sheryl (she's talking from experience, where you are just starting) (I once came from Ontario myself).
Unless you have some soaping experience under your belt, soap cooler. The hotter you have your lye solution and oils, the faster trace can run at you(some white florals, these are the worse, will give a soaper a fast run for their money).
So, I always recommend that new soapers start at body temperature, for both the lye solutionand the oils. Touch the outside of the lye container, it should be the same or slightly warm to the touch; and the oils the same. No need for thermometers.

If I have forgot to addresssomething, post back.

Sheryl said that she uses only 15 ml. per batch, I'm sure this is a typing error. I believe that she meant 15 ml. per pound of oils (which = 3 tsp. = 1 tbsp.). The amount would depend on which/whose scents a soaper uses, and how strong a soaper likes the scent to be.