Could I safely include the httpclient-4.0.1 jar that replaced the commons-httpclient jar that is now end of life or should I worry about having some conflict between both?
Some of my code is using commons-httpclient, should I be worried that having both would bring some problems?
No, you should not. HttpClient 3.x and Httpclient 4.x share no common dependencies beyond Commons Logging and Commons Codec and should be able to co-exist in the same class loader just fine.