1. I do not think you need 也 in this sentence.
也 means 'also','too''as well'
If you want this *and* that :我想买这个,*也*想买那个
2.It depends.Both OK in most sentences.
But 这*条*裙子 is better that 这“个”裙子
这(条)裙子不错,哪里买的?
你穿这(条)裙子很好看。
这(条)裙子很贵。
In informal chat, without ‘条’ the sentences may sounds a bit causal, just a bit.
On formal occasions, I suggested you use '这条裙子'
And I think these are questions about Chinese (Mandarin), not Chinese(other).