I wish I'd known that DNA donors have to be kept as family friends. I had DNA from all of the Lucky Palms elders, who have some interesting genes, but Eva was the only one who was friends with them and she died first. Goodbye samples

. Fortunately, I wasn't relying on them and had plenty of others – the Carrs ended up with DNA from twenty Sims, even after losing those samples.
I left all the tombstones in the mausoleum to start with but later sent someone over to collect all of the donors who were left, as well as quite a few other original townies. They stayed in inventory for a while, then were moved to the family graveyard. VW took DNA samples from several ghosts.
I did know about travelling causing problems, fortunately. VW went abroad a couple of times but left her DNA samples with Minnie. They survived being in a different Sim's inventory perfectly happily.
Clones' traits are a bit odd. Perfect clones are supposed to have two of their donor's traits, although I had two who picked up a random one instead (neurotic in both cases). It can be any trait, not just ones that are age-appropriate.
Good clones get traits that EA considers to be positive: artistic, good and/or flirty. Have to disagree with them on the last of those: the flirty trait's a pain, especially in a dynasty. Not to mention being wildly inappropriate for a baby

. They're also often born with the Attractive LTR, which is useful if a little inexplicable.
Bad clones are supposed to get two 'bad' traits, selected from evil, couch potato, coward and childish. (Why is a childish baby a bad thing?)