How to format the items for a checkbox field ?

Hello,

i am creating custom field and i wonder :

1/ How do it's better to format the items for a checkbox field :
- Did the title and value can contain accentuated letters ? space ? other special characters
http://awesomescreenshot.com/08431gfa19
- To be well searchable, it's probably better to maintain space between words in values ??

2/ I have checked my database and found this :
http://awesomescreenshot.com/0b831g92b5
For one checkbox field the values are stored 2 differents ways in database :
In one case the values are separated by comma... in the other case not !!
is it possible ? what is the correct or better one for future use ??

Thanks in advance for you help

Loïc