I don't think there are any legal requirements, but speaking the language is a good starting point. Join wwwthepoultrykeeper.co.uk There are quite a few ex pats on there who will give you sound advice.
Just remember though - the grass isn't any greener.
Speak French. It's vital. Depending on the size of and what you plan to do with the smallholding, there are all sorts of grants and other forms of help available but this is not Britain... all the information, courses and help will be in French.
French bureacracy is bad but it's something you simply accept because it is part of what the country is. With the right approach and language skills, most "civil servants" are very helpful but something we've particularly encountered in France is "you have to ask the right question to get an answer". If you ask if you can do xyz, the answer may be no. If you then say that you really need to do xyz, how would the CS recommend you achieve it?" you may well get a positive answer.
There are many things for you to consider - not least, employment because unemployment is high and the French employ French people first - but a big consideration is health care. The French healthcare system is excellent but following implementation of an EU law last year, unless you are covered by a certificate from the Department of Work and Pensions at Newcastle (E106, E121 to give a few) you need to pay for your own private medical cover unless you have work in which case you'll be paying high social contributions which cover healthcare. Depending on age and existing conditions (which insurers may refuse to cover) this could be an extremely expensive outgoing until you reach the UK state retirement age or possibly until you have been resident in France for 5 years.
If Admin here doesn't mind me recommending another site, you could go and trawl look at http://www.totalfrance.com/france/forum/index.php because you'll get a lot of good (and bad!) information from there. There are several sub-forums which will be of particular interest to you:
Avoid Postbox and Chatterbox unless you feel strong - it gets rough in there.
There's a search function on the forum and most of what you need to know has already been asked somewhere.
Finally, bear in mind that - depending on who you read - somewhere between 30% and 50% of people who move to France return by around the 3 year mark. France is just another country, one I love, but it's by no means perfect.