Since you are using such a high amount of CO I would certainly age a min of 6 months. I make my soleseif bars with 35% CO or preferably PKO mixed with shea, lard, and other soft oils aging 4-6 months. I do not find that salt makes a big difference. A 12+ makes any brine, salt or high butter bar even better. Also, if a little undissolved ends up in your soleseif bar it is no big deal, it will be finer salt than you would have in a true salt bar and dissolves as you use the bar. But do cut as soon as set or you may not be able to cut your bars. This issue is really trial and error.
On the other hand, my salt bars are 85% CO/PKO split without any butters or lard, the remaining 15% is 10% castor and 5% liquid oil. I always use 100% extra fine salt, usually Pacific sea salt or a mix of Pacific sea salt with table salt. Never never Himalayan Pink Salt. FYI I have been making salt bars since I started making soap so I can say I probably made every mistake there was to make with salt bars.
ETA: I just reread your post. Make sure you dissolve your salt before adding it to your lye. I am not sure from your post if you did that first. Also, water will only dissolve a 25% salt load and will dissolve better in warm to hot water. If using warm or hot water remember to cool the water back down before adding your lye or you risk a volcano. Soleseif bars are a good time to incorporate Himalayan Pink Salt if you want to use Pink Salt since you are using dissolved salt crystals. I used to always keep a big jar of it on my salt to have ready for use. Do not use the bottom sediment that you will see, it is undissolved minerals and clays which are scratchy.