i have a question, about a tattoo (in General)

sorry, for the lame question.

how much damage will a lesser steel familiar level 3.550 do?

So familiars (lesser or normal) have a DD spell of the appropriate type trained to the level of the tattoo. You'll have to find someone with a MM about that size (or someone who actually knows something about MM's damage ratio) to find out how much damage it would do.

That question is quite hard yet simple to answer, the level of magic missile it casts is 3550, which has a certain damage it deals.

however, how much damage that is, I don't know, some others might but damage depends on level so it could be hard to get an exact answer.

also that damage can be lowered by a number of factors:

Antimagic Field
Protection
Enchanted Armor Class: the (+x) on armors
Phantom Link

so i should just stay with my tattoo that increases my DX and ST?

Yes, stay with the tat you have until you have enough to buy a normal (non-lesser) tattoo. Buying a tat that is higher than base is almost always the best choice, as it doesn't take much longer to save up for a 100k tat than it does for a 0 level.

how do you get a tattoo, without bidding on the auctions page? there must be a source where people get them from

you can make a post in FS/WTB to let others know you are interested in buying one. Other than that regular tattoos spawn randomly in auctions only.

Auctions IS the source. All rares spawn directly into auctions.