Learn English – Using both past and present tenses in one sentence

The tenses in all your examples are perfectly fine.

I believe that in the last example you could have switched to present perfect if you wished so it would look something like:

Mike asked why you didn't come to the party with me, but I explained to him that you have been working hard for the past two weeks, and now you're free all you want to do is get some rest.

(I hope I got my present perfect right, I'm not too hot at grammar terms.)

Note that you probably want to say 'but I told him it was because...' or 'but I told him that it was because...'. In the final example you wouldn't normally have 'me' twice in the first part, you'd say 'Mike asked why' or 'Mike asked me why you didn't come to the party, but...'. In casual speech you'd probably get away with it, though.

Your last sentence using the future perfect simple tense( future perfect tense) is adequate for the following reasons. 1/It describe an event in the future that hasn't happened and is in no way planned. 2/Said(anticipated) event take place prior in time of the stated time of recollection."for the next year" However, since you used "for the next year" as your designated time of recollection therefore it is slightly more appropriate to use the future continuous tense.(For more clarity and formality)