yeah , its possible to get them on free pull

the free pull count on howmuch u already spent on it

It most definitely can happen. I pulled a few of my rares through free pulls. To be specific. KT ORO, Gaikido, Mifune and Bee all through free pulls.

All the treasures work in the same way, so yes.
What changes are the counters that are set to 40 for two stars and 60 for 3 stars for common rares. Super rares vary from treasure to treasure.

i always get common rare from free draw or a rare when i miss any free draws for a day and use it another day i got ninjas like gnwtenten,asumawb,gnwkiba,orochimaru konohatraitor don't know it's my luck or not

Yes it is possible (pulled hashi from free).
Depending on your priority, single pulls would theoretically be able to save you up to 9 seal scrolls (if you overlap the magic number needed where you get lucky with a 10 pull), but then you miss out on the guaranteed ninja, as well as the insane amount of time single pulling would need.

Edo treasure is all but meta. Most ninjas are either too situational or just too weak to be competitive.

But back to your question... yes. All draws, be them 10 or 1, stack to get the rare / super rare.

wish they had a history count on how many seal scrolls used on each treasure :)