So I'm spending about 60 hours in Istanbul (first time to Turkey) at the end of the month but since I get in later in the evening it's probably closer to 48.
In any case, I am curious about a few things.

From what I gather, Turkey is a mainly cash based society. While I don't intend to go nuts shopping (maybe a few souvenirs but no knock-offs) I've also seen/read that credit cards are accepted widely even in the Grand Bazaar and Spice Market. Is this true? Otherwise, I planned on bringing about $120 CAD (about $2400 Turkish Lira) for the few days I'm there.
The only souvenirs, I'm looking at bringing are the copper coffee pots, coffee, tea and a few small things like candy and spices. I'm travelling with carry-on only so space is limited.

Another thing I saw mentioned on youtube was that if you bring in more than one mobile phone you get taxed because the authorities think you'll sell it there. I have an OG iPhone SE and cheaper Motorola. I can understand someone with flagship phones, but even these? My iPhone is my travel phone because of the smaller size and the Motorola is my main phone. My iPhone might even be able to pass as an iPod touch, but I'd rather be honest and not end up in jail or with a massive fine. I really just have it to check emails when near wifi and likely wouldn't even leave the hotel.
Anyways, is there any truth to this?

Lastly, I've seen market tours with guides. While I'm usually one that prefers to do things on my own, is this really worth it?

My plan on things to do (in no particular order) is: Hagia Sophia, Blue Mosque, Basilca Cistern, the Hippodrome, the 2 markets, the boat tour over to the Asian side and if there's time maybe the Istanbul Archeological Musuem.

Anything I miss?
I haven't seen anything mentioned on the Asian side, but am open to suggestions that aren't too far from the boat/ferry on foot.

I know it's a tight timeline, but I'm trying not to overload it with too much stuff or things that mean waiting in long lines.

Thanks!