Regarding reading on the same subject and over-dependence - I think it also depends how you approach a reading. Many approach a reading seeking answers for ordinary life questions:
should I phone Bob?
what would happen if I phone Bob? (try it!)
if I phone Bob and we go out, how will the date go? (you won't know if you don't try that, either)
etc.
Too much of that will lead to over-dependence, though the odd draw will not cause harm.
And of course, these questions - which look quite trivial like that - can be legitimate depending on the circumstance (say, you and Bob had a quarrel and you want to find out if it's the right time to break the ice). Or the person might be shy and in need of a boost: if tarot can help her overcome her shyness and pick up the phone, good for her, I say!
But there is another way of approaching a reading - particularly with oneself. I call this conversations I have with my card. I treat my deck, then, like an interlocutor and we talk. So, what do you think, shall I call Bob? Really, well, you seem to know what you're talking about, I was just not too sure, because Shirley told me Bob was still cut up about his break-up. Shirley fancies him for herself? Sneak! well, I can't blame her, he's gorgeous. He is still cut-up about his break-up? no, recovering. I should go slowly - ok, so what do you think, just a quiet drink after work, we'll take it easy?
etc.
Of course, overdependence can creep in there too! But it does mean you can explore a subject in a free-flowing way, much as you might with a friend. Sometimes I have arguments with my cards, and sometimes they shut up on me or start giving me nonsense - that's the point at which I say thank you and put the deck away (or angrily toss the cards back in their bag!!).
Particularly in periods of mental stress, I find this way of dealing with my cards both soothing and good to help me figure out some things. Generally! sometimes - well, I'm just too close to the problem, not objective enough and all the readings in the world, or even one, will look like nonsense. And the more they do, the more I ask. At that point I've learnt to take a break - and approach another reader!