Re: oil breather
no problem running wise but you will fail an MOT with it venting to atmostphere, not to mention theres a change you can get oil all over the engine bay. the intake may slurp some dirt in thru the breather hole so really that should be blocked up. also, if you really want to run with it disconnected invest in an oil catch tank, this makes it road legal (MOT pass) and will catch any oil rather than it going all over the engine bay.
ps, just noted your in ireland, not sure on laws about venting to atmosphere there but england its an MOT fail, probably the same there for your equivilant tests.