You want to build muscle, it's that simple. Building muscle while having your nutrition sorted will help you to reduce fat while not losing actual weight. At least in theory. In praxis, this can go both sides at first, but doesn't have to.

That being said, I personally wouldn't do HIIT in that case. I'd gravitate more towards one of the dumbbell programs (with Ironborn being the best of the three, imo), or a proper beginner's full body routine from another source. If you don't have access to dumbbells, or just don't want to hit the weights, the strength based body weight programs here are a good way, of which Spartan Trials is one. If you're new to training, it might be a bit hard at first, but only one way to find out, eh? Alternatively, you can choose a level 2 program to start out, and supplement with a challenge to get your pulling motions in. If you can't do a pull up, there's options to work your way to that,meaning: Aussie pull-ups, dead hangs, and negatives.

I also think 30 Days of Gravity is a bit easier than Spartan Trials, although it tests your endurance on some days. If you want to add cardio, aim for low intensity, like rowing, jogging, or cycling. Can't speak much for the meal plans, but if you take care that you get your protein in, you're already halfway there. Eating at a slight surplus might help, too, but that's something you might have to figure out over the first weeks.

Good luck.

Thank you so much for this, really helpful and inspired to get started! Much appreciated. Family commitments don't allow me time or money for the gym right now but I have dumbells, bands and a TRX so I'll give one of the Darebee workouts a try. Thanks!