1. Buying secondhand will cut the cost but might be a little difficult with a sizeable bump. Leave the dress to a week or two before or you may find it wont fit.

2. I think that's plenty of time.

3. Outside is fine if that's what you want. Is there a covered area you can use if it's wet? If not go for inside.

4. Don't touch the MIL. She could be right, but if she is you will have to fork out a lot less money which can only be a good thing.