Too many wordings vary from person to person, I'm just to name a few here.
All these wording above are common actually, and yours isn't so bad either.
③ is the most concise one within just 9 characters.
I myself would prefer to use ① or ⑦ which are sounds more literary and well educated.
- 知之甚少——知：know; 之：it; 甚：very, much, more than; 少：little
- 涉猎尚浅——涉猎：dabble, dip；尚：still；浅：shallow
There's a difference between the ③ and ⑦, you must be noticed there's no wording such as '对' in ⑦, and the subjective '我' has been moved latter, this will concise the sentence but it's not a formal use, yet still can be used in colloquial.
Speaking of 'know about things', there are many more expressions.
略知一二：Just know the first point and second point of something literally, which means merely knows a little.
But this can also be used for modest, someone actually knows a lot with a low-profile attitude
半桶水：half bucket of water
This wording derived from '一桶水摇不响，半桶水响叮当' which means a full of a bucket of water makes no sound, whereas half a bucket of water is easy to make noises loudly.
It refers to someone who is really erudite won't display too much, while someone who wants to pass for erudite and usually showing off their knowledge.
So '半桶水' can describe someone as a dabbler, or as a self-effacing wording to oneself. Say '我就是个半桶水', means 'I've learned less(about this)'.
Here are some other common idioms in which you can drill down if you wish.
Lastly, as for the 'about', '对' is not the sole answer, we use it a lot just for convenience, if we say something with '关于', it's likely to say 'pertain to' instead of 'about'.