In many of the stories about 千 (http://kanji.koohii.com/study/kanji/40),
I see it associated with needles.
Is 十 (ten) somehow related to needles?

針（はり） means needle

only thing i can think of is the 指切りげんまん嘘ついたら針(needle)千本飲ます song kids sing when making a promise. dunno if that's what the stories are referring to though.

edit: i had a look at the stories and it looks like people are splitting up 千 into the line at the top (which they are calling 'drop') and the 十 part which they are calling 'needle'. I guess it helps them remember it...

edit2: did some digging around on the internet and I don't think that 十 really has anything to do with needles besides being a component of 針. Well, one odd blog post about religion I found claimed the 十 in 針 does acutally mean needle (漢字の針は、金・十で、十は針を意味しているとされます). Another more reliable-looking blog about kanji says that the 十 in 針 represents a cross shape　(--> pointed metal): 『針（シン）』zhenは、針（はり）を表す形声文字です。漢字の足し算では、金（金属）＋十（十字状の）＝針（金属製の先のとがった針。はり）です。

well.... i honestly have no idea myself. lol. bye~

Yeah, what's basically happening is people are choosing to split '1000' into 'drop' and 'ten' which heisig gives another meaning of 'needle' based on the kanji for needle (hari). I'm pretty sure that he gives it the meaning of needle because needle is much easier to make a story for than '10'.

It's fine in general to split up 'primitives' or whatever if it's easier for you to imagine something using other elements, as long as it doesn't interfere with you remembering how to write it, or the meaning