The big decision before it's built (Apart from the colour) is whether to go for a dynamo or not, it's a much smaller upgrade cost than adding it later.
Once you have the bike, it's worth protecting where cables or luggage may rub with decent tape, I use 3M HS8671, there are others but not everything sold as "Helicopter tape" is the same.
Apart from that, I'd be guided by Thorn's vast experience, hope it's everything you wish for.