I was looking into cisco's documentation to find out if there are modifications in configuration when upgrading from 7.0 to 8.0, but I didn't find really much information.
I'm aware about the recommendation for flash and the recommendations if I'll do the Zero-Downtime Upgrades for Failover Pairs.
I wanted to know if will be configurations changes and if I can upgrade 7.0(x) straight to 8.0(x) with no worries
The link posted by Muhammad is a nice one and is oriented mostly to upgrading to 8.3, which is a big step and a lot does change there. It is not so big a step from 7.0 to 8.0. I can not say that nothing will change as you go from 7.0 to 8.0. I do believe that it is very feasible (and safe) to go from 7.0 to 8.0.
It is good if you upgrade from 7.0 to 7.2.x and then jump on to 8.0, you should face no issue with it.
If I decide to go to the failover zero-downtime i'll definitive do that, but id I choose not to do zero-downtime is there a reason for that ?
Yes, that link is great for 8.3 or even 8.4 i've used a couple times to do a few upgrades, but I wanted to make sure that no major changes on configuration happens in between 7.0 and 8.0, since cisco's docs dont say anything about I had a doubt.
I have a upgrade to make and it would be huge deal if anything changes.
Well if you go for zero downtime upgrade on failover pair or for standalone firewall, this is the upgrade chain that should be followed, doesn't matter if the firewalls are in failover or not.