The next decision that you have make is where are you proposing to keep them and which type of the 130 plus species do you wish to keep.
There are species that are only 5 or 6 inches in height to ones that are over 2 foot with all sizes in between.
 

But before you make these decisions my advise is to learn as much as possible about owls. There are a few good books about owl, these mainly deal with owls in the wild . Which you will have to have a good understanding of before you attempt to keep and hopefully breed in owls captivity.

Also, if you can, get to know a reputable established breeder and talk to them (in my experience owl breeders will talk owls all day long if you let them) and if you are lucky they may even allow you to 'help out' with their owls thus gaining valuable experience. But whatever you do - do not become a nuisance to them.
 

I would also advise joining a reputable organisation or society. One that I would recommend is 'The International Owl Society'. This society is dedicated to owls both in the wild and captivity, they also produce a bi-monthly magazine 'tyto' which is full of articles about owls, written in the main by owl breeders. They also hold regular meetings which, if you attend, is another way of meeting the 'expert' owl breeder.
 

Another source of information is of course the internet. Go to the search engines and do a search on 'owls' (you will have to sort the wheat from the chaff though as there are lots of organisations who call themselves 'owls' including a well known soccer team in Sheffield)
But having said that there is still a lot of information to be gained by persevering a little bit and perhaps varying your search criteria try using 'raptor', 'strigiformes', 'Barn owl', 'Screech owl' ect. and you will get the information you are looking for.
 

Right, you have now learnt every thing there is to know about owls. You have read half a dozen books on the subject of owls, you have plagued, bothered and interrogated any owl breeder that you could get near and you now have a massive telephone bill by spending hours and hours searching the internet.
 

Next decision, what species of owl do you want? it's no good reading 'Owls of the World' and deciding that you want to keep a species who's world-wide population is 6 breeding pairs-You just won't be able to obtain any. It is better to take advise from the breeders that you got to know from your learning curve.

The final choice of owl will depend on the availability of the owls themselves and the space available for the flight.

A table of the more popular species of owls and their required flight size is produced below:-

The availability of the chosen owl can be obtained from either talking to the breeder or if you joined The International Owl Society from their bi-monthly magazine 'Tyto' which runs a free advert section for members wishing to sell their surplus stock or from the weekly publication 'Cage and Aviary birds'
 

 siteing the flight