Christmas approaching

I decided to go for this compressor :
http://www.airbrushsupplyonline.com/compressors/mini-airbrush-compressor-with-tank-as186-oil-freeAnd the iwata neo CN (gravity feed) for minis painting, and detailling.
BUT...But I made some searching on internet, and I saw a lot of people using a bottom feed airbrush for big projects, like big kit models, scenery, etc...
It seems to be more easier to keep pre-mixed bottles of diferent paints (for example, one bottle of green for bases, one bottle of grey, one bottle of brown). IS that true ?
My main goal is to paint scenery and minis base coating, and sometimes a big monster (dragon or things like that) or battletech mechs. But mainly, scenery and minis base coating. I've got tons of delayed work to finish, and they are all scenery related.
I'm also thinking that maybe I could have a side small business making scenery (as I did in the past, perhaps some of you have some of my work on your wargaming tables

), so I would use often the same paint schemes on pieces (I'm currently unemployed, tough economical period here in France

).
So do you think, keeping the iwata gravity feed airbrush for fine jobs, should I add a cheap bottom feed dual action airbrush + a set of spare bottles would be usefull for my needs ? what size of needle ?
Or maybe, should I go for only one relatively good bottom feed airbrush (IWata Neo 0.5mm bottom feed version ) ? Since I will be using a 3l tank compressor, it should give suficient pressure for bottom feed ?
thank you for your help.