Kings Cross to Heathrow is easy. Just take the Piccadilly line straight, but note which terminal you are going to (I imagine, either 2 or 3 - which means get off at terminals 1, 2, 3 stop, or the later Terminal 5 stop). If you allow yourself 1.5 hours from Kings Cross (the journey will not take that long), it will help calm nerves that you may be late.
Some things for Ferrol that I did the afternoon I arrived, as I was dead nervous the evening before.
1. Realise that unless you venture to McDonalds, it is almost impossible to find an evening meal before 8.30pm.
2. I spent the late afternoon time walking the first 2 km of the Camino Ingles from the harbour through the old town, which meant that I could then just step out of my hotel next morning and join the Camino from where I left off, and it also cut 30 minutes off the long day to Pontedeume (if you are going that far).
3. I obtained a stamp that afternoon (dated next day if you want) from the tourist office next to the harbour (open 4 till 6pm in the afternoon). The tourist office only opens at 10am in the morning - too late for starting the Camino tomorrow. The tourist office also has credencials if you need
4. For good measure, I also obtained a sello in the morning from my hotel in Ferrol. Most hotels should be able to do this, and many in Ferrol also have credencials.
5. Went to the large supermarket at El Corte Ingles, to stock up on drinks and other provisions for the next day. The supermarket opens till 9pm, but again, only opens at 10am in the morning.
6. Looked round Ferrol, including the cathedral, which the Ingles walks by.
7. If walking all the way to Pontedeume, consider taking the short cut over the N-651 road bridge to Fene, as the first stage is very long. If you do this, you will still walk 100km from Ferrol to SdC and be eligible for a compostela (provided you have the minimum of 2 stamps per day).
I was also completely nervous on the first day. I am in my 50's, did no special training, and therefore, if I can do the Ingles in 5 days, anyone can. The stages are long, but the uphill bits, in the main, come at the start of the day. The one thing I found was that shops, bars and restaurants were not as frequent as you imagine encountering, so I needed to stock up on things to eat on the way (including some bread and meat for sandwiches), and with ample rest, you make it. The longest stage was 9 hours, but at a steady, not fast, pace