looking at some of my showwinning highland ponies parentage, they have fathers on oneside who are grandfathers on the other. i asked an experienced breeder if that was ok when i started up and was assured me it was fine, as some people breed alot closer.
going for a wider genepool also means ur offspring are likely to be less uniform in appearance.
line breeding should give u offspring that are similar. its possible to develop ur "own type" of pedigree animal if u consistently select the desired traits.
breeding v close means you can fine tune any particular conformation traits, but it also exaggerates any bad points so u need to be prepared to cull the bad ones.
i was lucky with getting our ram as we got him from an experienced breeder with several lines, who knew our bloodlines and she chose him to compliment our girls.
i personally think cousins is close enough unless u know what u r doing, then id get the best ram u can and only register the best.
on the otherhand where people do well in the showring, they can stick to the bloodlines that work for them to the detriment of the genetic health of the animals. we had a welsh pony from a topclass breeder (regular hoys winner) this pony had a genetic disorder which resulted in her foal being pts at 4 weeks. when i informed the original breeder, she didnt give a shoot, as her pony had won hoys the week before. personally i think health comes before beauty, but if u can tweak things to get get closer to the breed standard then go for it. with farm animals u can eat ur mistakes so to speak.