There are 2 main decisions to be made...
Size of internal memory - 16 / 32 / 64 gigabytes. If it's just going to be used for emails & web access, 16 gb will be fine. If you envisage storing downloaded films / TV programmes, or a large music collection, then probably 32 gb would be better. 64 gb if a large number of High Definition stuff is to be stored.
Connection type - WiFi / 3G / 4G - the basic model comes with WiFi only which is fine if you're only going to use it at home with your own WiFi signal, or at any spot where WiFi is available (e.g. hotels, cafes, bars etc). The models with 3G / 4G will connect via a mobile phone signal, but this incurs extra costs and currently I believe it's quite expensive.
Someone else will hopefully advise ref Excel / Word etc - but my view is that if a lot of work is going to be done on these applications a laptop would be a better choice.
No idea at all about controlling the lights!
Hope this helps