There’s no reason either a lemon drizzle or coffee and walnut cake couldn’t be covered in fondant. Your fruitcake is certainly sturdy enough to handle a 2nd tier. Make few more fondant roses to adorn around the top and bottom tier. Perhaps a few roses on top of the cake.
If you add an additional tier, make sure to add some kind of support sticks into the lower tier. I don’t understand why you want to cover the cake in both marzipan and fondant. I’ve never used marzipan, but I would think that you would use either one or the other. Maybe others can advise on that. Also make sure that each tier has its own cake card underneath it.
The Garden Baker, it’s traditional to cover a fruitcake in marzipan, and then usually the fondant covering is very thin. And Garden Baker is correct, your 2nd tier needs to have it’s own cake board. And you need to put dowels through both tiers, with one central dowel in the middle that should go right through to your main cake board. Since the fruitcake is quite dense, I personally would use sharpened wooden dowels. This will ensure your cake with be sturdy, won’t slide, tip, and be safe to transport.
Thanks everyone for your replies. I went for a lemon cake on top of the fruitcake in the end. I was quite pleased how it turned out for a first attempt!
Your mum willed be thrilled. Your roses are great!
You did a beautiful job!