Totally confused on this incursion and temple

I want to level Alva for the hideout decorations she has (she has the old graveyard decorations I was working toward before they removed the masters) but wow wtf is up with this incursion nonsense?

I read that in order to make the completed temple high level you have to do the incursions in high level maps. Well I found Alva at level 60 in a level 50 act and accepted her quest before I read that.

So first question is did I already screw myself? I don't want to do the incursions at a low level if it means the temple will be low level. Can I just forget I took this quest in a level 50 map in act 7 and wait until I'm running high level maps to start doing incursions?

Second question is is there a way to buy her decorations before running the first incursion? I'm assuming I should wait to start doing them.

Permanent screwups are nearly impossible in PoE.

You didn't mess up anything. You run enough incursions to open up the temple, run it, and then it resets and you do it all over again. And again.