I find female ISTPs intriguing and am curious about how they tend to act
Quiet, contained, and assertive. I wouldn't say she's shy at all, from detached observation or from what I've known of her. She's polite to strangers, but otherwise treats everyone equally. The IXFX types flock around her like moths to a flame, basking in her "aura of self-confidence" and sing her praises from a safe distance. We haven't been going out for that long - nearly three months - but I can't help but wonder what it is they find so amazing about her. She doesn't do anything; maybe it's just the way she carries herself. I dunno. She jokes about it "boosting her already inflated ego", but it makes her a little uncomfortable, I think.
what they tend to value
Space, space and more space. Shared interests are also a bonus. A partner who isn't sensitive so they can use your ego as a scratching post.

Kidding. But if you don't like being teased, then you may have a bit of trouble. Luckily I'm the one who pwns her at banter:
ISTP: Well send [Housemate] my condolences
ISTP says: Your mom broke him
INTP says: Is that so?
ISTP says: Broke him like a bronco
ISTP says: Yeeeehaw
INTP says: she couldn't be with him last night
INTP says: Because I was.
ISTP says: Spoil sport......WHAT.
ISTP says: [housemate], I THOUGHT WE HAD A DEAL
INTP says: OH HE TOLD ME ALL ABOUT YOU
ISTP says: NOOOOO
INTP says: Apparently he's been with a lot better.
ISTP says: D:
INTP says: I think his exact words were "barely average".
ISTP says: DDD:
ISTP says: DDDDDD:
ISTP says: T.T
INTP says: At least that's what I thought he said. He had his mouth full.
ISTP hangs self
ISTP says: M-m-maybe you misheard?
INTP says: Dead people don't talk.
This is how we usually begin a conversation. Always with the "yo mamma" jokes. Tsk. When will she learn? Never challenge an INTP to a game of banter. You will always lose.
how they are perceived in a relationship. So female ISTPs (or people who have dated them)
Offline, she acts like a friend. We chill out, go watch a movie or eat icecream. Which is cool. She'll have her once-in-a-blue-moon snuggly moments. But otherwise, you would think we were a couple of friends hanging out.
When we talk online, which is a lot more common (See: IXTP need for space), well, see above. While we chat on Skype, she's sending me links that Imustclicknowomgsocool. I'm a little more affectionate, verbally:
INTP: <3 Missed you~
ISTP: How was your day?
I remember within the first week of going out, she said to me through an email, "I just thought I'd let you know that I'm head over heels for you". Which made me doubt her type, if I'm honest. Either that, or I witnessed a burst of inferior Fe.
She likes to draw. She sent me an email on Christmas morning, with an adorable picture of an echidna. A note saying, "I thought of you and doodled". She knows echidnas are my favourite animal. Sweetest thing ever.
what types do you usually go for, are you more attracted to thinkers or feelers, do you like to be in charge, what are common positives / negatives you tend to encounter in relationships, etc, etc, etc.
She comes across as "passively dominant", if that makes sense. There is no real power-playing in the relationship, but she likes to call the shots in terms of communication - she initiates and I respond. I like this system because that way I know for sure that she wants to spend time with me, plus I'm happy enough to do my own thing. The odd hello is enough for me, really. I have my own distractions and so does she. I think that's why it works.
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Content may not apply, as we're both young (eighteen).