I'll try to share what I have experiences, I don't know what is and isn't allowed in challenges as I am lousy at following rules, so they won't work for me
Whether you create a family or play a townie one, the rules still apply.
Jones family, lives in SV, has a son and can't find a mate for him. I decide to move the family to RV. Save the game as SV Jones 1. To make sure I don't goof up I play for a few more minutes and save as SV Jones 1.1. You can use the phone to move to another town, or use the save to bin and then transfer them.
I am going it works both ways what happens with what you have. If you sell all of your items, you will go without anything. If you want to save it all, best bet is to move to an empty lot, save again, and then do the save to bin.
Choose a new game with the town you want, RV. Start the game as normal, but use the adding a family. Pick out a house and put your family there. If you have saved your stuff, you will, generally, find it in family inventory. I have moved and found items missing, when I move other times when I move have it all.
If for some reason you don't want to play in RV and want to return to your previous game you can just go back to it. You have saved it and it will show up in the boxes when you go to play (I'm not good with technical name of stuff) choose that save and you will go back to the save.
You will have lost all of your wishes, opportunities and relationships with anyone in that town. But you can continue as if you haven't left the game. If your sim is employed they should start back at the same level, I have had a couple lose a couple levels.
If you return to the old house and didn't sell the items, they will still be in the house. You can end up with duplicates.
For dynasties, I don't know the rules, so you can ask those who are in charge of them and they can answer them.
Hope it helps, I try to do several saves in a game in a town.