Newbie upgrading iphone - saving data?

Hi All

I have an iphone 8 on ios 13.7, it is all backed-up to the icloud. This iphone is about to be sold.

I also have an old iphone 5 (yes 5!) on ios 12.4.8.

I will be transferring my iphone 8 SIM to my iphone 5 so I still have a working phone. I have tried this and it works well - all apps and services are good.

However, I can not recover my data from the iphone 8 (on ios 13) on to the iphone 5 (ios 12)as it is not a compatible back-up. I am okay with this as the iphone 5 is only temporary.

I intend to buy an iphone 12 when they come out - which I presume will be on ios 14

My questions and help requests are the following:

1. Will the iphone 12 (ios 13) be able to be restored from the iphone 8 (ios12) back-up file?
2. How could I recover the txt messages received on the iphone 5 (ios 12) during the interim period to the new iphone 12 (ios14) when i get it? (other apps won't have data i need recovering I don;t think or are back-up else where).

Thanks in advance for any help.