Acer negundo, according to one site is of 'easy cultivation'!
Acer negundo - Plants For A Future database report
I assume that flamingo is a non-green cultivar - these do tend to be weaker than green ones (reduced chlorophyll therefore less photosynthesis therefore weaker growth) and therefore the previous advice about avoiding shade is important. Otherwise Acers as a whole are not difficult to grow - we have a miniature reddish one which is heavily shaded but growing happily on about ten centimetres of water-logged soil!
Acer spp do suffer from a lot of pests including slugs &c - maybe growing it on in pots for a year or two to allow it to build up branches and roots would be a good idea before planting it out in a well-prepared site?