It's ok for them to go under furniture as long as there's nothing they can hurt themselves on/ that could fall on them. Be warned though that they may not want to come out so make sure you can safely reach them or you'll end up with scared piggies when you're trying to get at them for bedtime. Also, if they decide it's a comfy place to set up camp then they are likely to pee/ poop under there. I'm sure you already know this but I wouldn't try floortime until they've settled in for a few days.
As you've pointed out, it's really important to keep wires out of reach as piggies may chew on them. You can tape wires up or cover them/ block them off. I have used correx about 20cm high (thick cardboard would also work) and taped it to the skirting board so that the wires are completely covered (ask your parents first because it might damage the paintwork). I also use a pile of books to restrict access to another area where I can't make it safe.
Great to see you considering all this stuff before your new piggies arrive. Not long now.