Welcome aboard, Nick, congrats on taking the decision to change your life for the better. Sounds like you are determined and focused, so I see no reason you will not complete the 8 weeks. The first few weeks are the most challenging and once you have those cracked the rest will probably fall into place quite easily.
If hydration is an effort for you, I suggest starting to tackle that now, in your build up to you full on start. Have a think about what might work for you – using a drinks bottle to drink from, so you know how many you need to consume a day; draw a little chart somewhere to record each drink you have. I draw little cups and glasses on the white board in our kitchen and cross them through as I have each drink. You just need some little reminder, so that you increase your intake and can see what you’ve consumed.
This is also a good time to start to clear the cupboards and freezers of non-BSD food, as far as possible (assuming there’s no one living with you that will want such things) and think about what essentials you’ll need for 2nd Jan. Try to keep BSD friendly foods around which don’t require too much preparation, for those times when you need ‘a little something’ or a situation arises where you’re not able to use the planned a meal. If you feel the 8 weeks might be a bit challenging, join the next 4 week challenge on the forum. This is just a group of forum members who tackle the BSD in four week chunks, as opposed to the standard 8.
Maintaining your muscle mass should not be an issue, as long as you keep up your exercise and ensure you are including a good amount of protein in your meals.
Make good use of the forum – use the search box in top right of page to search for specific topics – there is a lot of wisdom and experience on here and people are happy to offer advice, support and encouragement, so just shout out. Definitely post all your results and let us know how you are getting on. I haven’t put anything in this post about my person stats and journey, as it is all documented in my profile, if you want to take a look.
Best of luck to you on successfully changing your life with the BSD.