The only problem besides the top dressing, I see in this pic, is you left the MILK out!
You'll want to visit the tropicals part of the forum for specific help, I would kill it indoors.
There'll be lots of info to search on ficus there.
To make sure I'm understanding this correctly, you're saying to get rid of the pebbles (muck) immediately and that the wiring may be necessary regarding the juniper because of the windswept nature of the plant if the root system isn't sturdy enough to hold it upright?
Will simply removing the pebbles be sufficient at this time or will I need to supplement the space with a new soil or sphagnum moss?
Yes replace the sphagnum moss and pebbles with just a little bag of pebbles or you can order some bonsai soil
to replace the top dressing, and will have it on hand for Springtime repot too. Windswept or not, which it is not ATM.
You just don't want to remove the glued in muck, and have a plant that will blow about in the pot at the will of the wind
or every time you touch the pot, and dislodge new roots damaging them. You want the trunk secure, so if you must
you can even wire it up through the bottom of the soil through the drainage hole(s), which is less conspicuous than
the 1st idea I put out there to wedge on top of the soil and anchor that to the entire pot, but it works.
I use bonsaijack.com for my soil, but you may have good local sources.
Too, join a local bonsai club. We have none around here, so if you find a GOOD one they too can help
with hands on experience.