Wilton has a tip 86 that pipes a ruffle and a border at the same time, but its a star tip, not plain. Maybe you can find one similar with a round tip, now that you know what it looks like. Ateco also makes fancy ruffle tips.
You can definitely use any kind of smooth jelly that you heat up. If it is a powdered sugar based BC, it's likely crusting. This means that the icing will form a crust so it won't be sticky, which is desirable for many techniques. But when you need fondant or marzipan to stick to it, you need to add moisture so it will stick. If you tried to apply the marzipan on the crusted buttercream, it would just slide off. If the buttercream crusts, you will know by lightly touching...
No pain at all. The truth is I half forgot and half am super busy! So here's the situation, I piped this at the studio, then packed my tools in my car. Then I moved to a new house and packed a bunch more stuff into my car so I will ge to it. Off the top of my head I think it is 1B? I will dig it out, sorry everyone!
Marzipan will not stretch like fondant, so the application will be different than fondant. I recommend you do get a second smoother eventually, but for this application it may not be necessary.
I would roll out the marzipan with powdered sugar underneath it and cut panels to apply to the cake, trim them to fit. You can use your smoother to press it onto the cake so you don't get finger prints.
As for the jam vs BC, what kind of BC are you using? Does it crust? If...
I personally substitute pureed fruit, like pumpkin, banana, or apple sauce for eggs all the time. In a chocolate cake mix it will not change the flavor or color, but in a vanilla cake mix you will notice. It makes the cake denser and it does hold together. I actually prefer subbing pumpkin in brownies since it gives them a nice dense fudgey texture.
I have used enger-g egg replacer and do not like it as a sub for eggs in a layer cake, it just doesn't hold the cake...
That Meringue Crusting BC recipe sounds like what I had on some cookies recently and I have been trying to figure out what it was. They were the best decorated cookies I ever had. Can't wait to try that recipe!
NOOOOOOOOOOO! IMBC can almost always be saved. So sorry you didn't get help sooner. Search in the top right corner of the home page for IMBC troubleshooting and you will find many threads discussing all the potential issues with IMBC. Next time, save it.