When you apply for the DVM the way they weight your scores means that first year marks count for a lot less than second year marks (or aren't counted at all if you're applying at the end of third year) so try not to stress too much! They know that especially for your first semester your marks can take a dive in first year as you adjust to uni and also that you cover a lot of content that isn't really relevant to vet, so they care more about what you do in second year.
My understanding if yes, for a guaranteed place you would need to get a 70% average across your level 1 subjects, but if you do well enough in your level 2 subjects then you might qualify through the normal selection process even with an average below 70% across first year. If you don't get in at the end of second year you can definitely apply at the end of third year where they don't even look at your first year marks. People have got into vet through all sorts of pathways so even if you don't get in at the end of your BSc then there are other paths you can take.
I wouldn't give up on getting into DVM just yet, but for the sake of answering your last question I think you need to think about what aspect of being a vet you would like the most- if you want to be interacting with animals then vet nursing is a great option, if you like problem solving there's sooooo many jobs you can do, if you like research there's jobs in areas like animal welfare and agriculture...
You still have plenty of time- try not to panic and just do the best you can