drag and drop Overhead needed? Can flash card type create errors?

I am copying nested folders of text files (LWP, Word, JPEG) from my hard drive in Windows XP SP3 to flash cards.
Sizes range up to a gig or so with about 30,000 files.
No problem with shorter files.
No problem with nested folders of JPEG.
On larger nested text folders, the size of the copy is larger than the original. I also found this in copying onto WD 1 ter and 1/2 ter external hard drives.

1. Am I right in thinking the additional size and number of files is needed for the directory in the target media? I call this overhead in the target media.

2. Copying 1 gig nested folders with about 30,000 files onto a Verbatim 32 gig flash drive with about 26 gig free, Properties reported the copy to be smaller and have fewer files.
Same original copied onto 128 gig mini Sandisk flash card with about the same free space resulted in larger copy on target media. Most of the used space on the Sandisk was taken up by nested JPEGs, and the nested files were shallower and smaller than the large nested text files.

3, In one case (large nested text files onto Verbatim 32 gig card) after copying the original was smaller. Any idea what happened?

4. How reliable is Properties? Except for this one instance, it seems consistent.

This is all on a Sony Vaio about nine years old that, I understand, is nearing the end of its MTBF.
I will replace it but in the meantime I want to get all my files copied.
Flash cards are unreliable for long term storage. I have found that I needed to format them everytime I wanted to write new contents onto them to avoid data corruption.

Anyways to answer your question, flash drives don't work like hard drives b/c unlike hard drives, the flash drives write in blocks of data. Say each block on the flash drive is 500kb, even if your JPG file size is only 102kb, it will "occupy" the entire 500kb block, which might explain the larger space.