1. Is that all there is to it? I thought it was much more complicated than that.
I'll change some words to their contracted forms for more conversational speech:
2. If that's the way you feel about it, it’s no use my saying any more.
3. It’s like this: you don’t want to go and I don’t want to go, so why go at all?
4. I've come to see you about some books you mentioned in your catalog.
5. I’ll just run and get some cigarettes. I’ll be back in no time at all.
(Depending on where the person is going:
I’ll just run out and get some cigarettes. I’ll be back in no time at all.
6. It’s as simple as this: you just don’t have to bother your head about it.
The sentence is a little odd. The first clause suggests you are going to spell something out for them, but the second clause is really more a dismissive remark that would be made in its own right, as a retort:
"If that's how you feel, then just don't both your head about it any further!"
7. It’s about the best way I can think of doing it. If it doesn’t suit, you can ask somebody else.
8. She has enough work to do as it is without being saddled with any more.
9. There’s nothing like a nice coal drink on such a stifling hot day as this.
(Each to their own taste. Is this some form of ersatz coffee in Bulgaria? Over this way, we would prefer a nice cold iced coffee.)
10. It wasn’t long until we heard the front door open, and soon after, there was a heavy thud in the hall.
(check the difference in meaning between 'after' and 'afterward')
11. It sounded exactly as though the roof had caved in.
12. Within a few miles from town, families on tenant farms were huddled around fireplaces in drafty hovels.
(The two clauses seem oddly juxtaposed as they stand. Consider:
Within a few miles of the town, families on tenant farms were huddled around fireplaces in drafty hovels.
If you have been referring to 'families in the town proper', then I would write:
Within a few miles of the town, the families on tenant farms...
13. Food and clothing were scarce, and in same instances, nonexistent; jobs were rarely to be found.