Jumping in with both feet but I need some input

I've decided that I really must try my hand at mail art. Two things have held me back from trying it. One, I couldn't come up with any kind of "theme" that really appealed to me and two, I'm not the most artistic or creative person. The first obstacle I've managed to overcome but the second one has me feeling pretty shaky.

I was the kid who got glue in her hair in Kindergarten. And I was the kid with marker all over her face, hands and arms because grace certainly isn't my middle name! Alas, I was also the kid whose eyelid got glued shut when she turned in her seat to say something to a friend and bumped into said friend's raised rubber cement brush. I haven't forgotten those incidents though the traumatic aspects have faded. Ha!

Paper, pens, pencils, stickers, crayons, wax, markers, tape, and yes, even glue, have been lifelong loves of mine but only in a sit down, write a letter, glue or tape the flap of the envelope if needed, seal it prettily, and mail it sort of way. I've never taken it further though I've felt a strong desire to do so. Finding all the wonderfully creative mail art bloggers out there has deepened that desire and I've been torn between wanting to dabble and wanting to tear my eyes out so I can't see all the pretties! The pretties won.

This morning, as I worked with a faded, smudged, printed census record, eyes squinted, magnifying glass over a very hard to read name - it hit me. Why not use my love of genealogy in my attempt to create some kind of mail art? 

I like that idea, I really like it! I even have a picture in my mind's eye of an envelope I want to create. The problem is I'm not sure just where to start. 

I know how to make collages and used the concept to cover the counters in a business I co-owned a few years ago. The result was lovely and received many compliments. I have a nice collection of pens, markers, and other writing instruments and I have more paper than the local library, I think. What I lack is basic knowledge on how to pull those things together to create something from nothing. 

For example, if I want to make an envelope, can I/should I use an existing envelope or is it best to start from scratch and make one? I've collected some information on how to make envelopes but don't know if an existing one would work. 

Okay, so for you mail art and creative folks out there, how should a newbie like me start? I really need input. Thank you!