You do not need plat, though it IS cool to have a premium char, especially if you will ever buy auction slots. Most of the costumes can be purchased with gold and you can mix and match them -- head, shirt and pants. You can get extra character slots for free if you have additional email addresses.

If you work on timing your feeds, you should not need that many blood packs. You can also farm for gold and/or blood packs, of course.