In the last example the request (will you?) is very informal and not very polite, you say that when you expect people to do stuff for you (like when you're their boss) the second request (could you?) is polite and so can be used in wider range of contexts.
If I had- second conditional, hipotethical situation (he doesn't have nor expects to have money for a car any time soon)
If I have- first conditional, he may have money in the future
secluded and isolated- I am not sure here, but I guess that secluded has positive meaning (like the house is far from all the noise of the city) and isolated is negative (it can be dangerous to live in an isolated house)- so the difference is in tone- one has positive and the other negative connotation.
Get Swan - English Grammar to find out more about conditionals, the book is very useful for grammar:)
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