Usage of Scarcely, Barely and Hardly (ever)

I learned a new grammar with these adverbs above (in the title), so I hope you correct my sentences bellow:

Remember to leave spaces after brackets or commas.

1.They are scarcely interested in your spiffy haircut.

Here, interested is acting like an adjective, so use the verb ‘to be’ to make it a working sentence.

3.tThe economy had hardly haexperienced downturn before the goods tripled in price.

‘Had downturn’ sounds a little off in this situation, this sounds more natural.

4.Hardly had the economy had downturn before the goods tripled in price.

While this is okay, the word order is considered archaic (old-fashioned), so “The economy had hardly experienced downturn before the goods’ prices tripled.” sounds more natural. :)

5.It's hardly weird to see James running around barefoot,because the grass is so soft.

While grammatically correct, a little bit of emphasis helps this sound more natural.

7.BareOnly three of my friends, including me, had been waiting for him for a month whenuntil he was discharged from hospital.

Firstly, I think I only works better here, as a more natural word, and also, I think the actual meaning is conveyed a little poorly. Consider commenting a rewritten form of the sentence. :)

8.The side effect had no sooner occured than I had vomitted on the floor.

“Had” is being used for the pluperfect tense here, contrasting it with the time period when the “side effect” occurred .

I need to mention I used Iinversion in some sentences.

2.His parents hardly ever permit him to transfer to another school.¶
¶
His parents would not permit him to transfer to another school.

It is little unclear what this is referring to, as the phrase “hardly ever permit him to” would indicate a reoccurring event that his parents generally will not (but not never) give him permission to do.