This has been said severally, Nigeria is a consumer nation, even things that we can produce here are been imported, just imagine going to purchase goods from another country, you will have to buy dollar first before they can allow you to do such, even in Nigeria here import duty is been paid in dollar, somewhat do you expect, another aspect is hodling of dollar by our politicians, if a thorough search is been conducted in must of our politicians house, the amount of dollar that we will see will surprise many of us, and again if someone import goods to Nigeria in dollar, you don't ecepevt such person to sell at a cheaper price a few paying a high import duty and clearance fee.
Exactly, the way naira is been presented is actually what affects it. Naira isn’t treated as a currency that should be regarded for storage. This can be done just as you said by not only using the dollar currency for every transaction but also the naira should be used. Imagine having to sell our crude oil to another country using another currency which is not suppose to. You need to give people reason to hold your own your own currency before it generates value.
Another reason why Naira also depreciates is the excessive printing of its paper money, most top currency in the world mostly put regulations in the number that should be printed so as to have a limited number of that currency but that is not it.
As to OP what actually set the price of things high when there is always dollar price increase is sometimes people selfish interest there are some markets that dollar hasn’t actually touched but they are increased due to others increasing there’s and not necessarily the dollar affecting it