You don't really need consultancy to set up DKIM and SPF records.
SPF
https://support.google.com/a/answer/..._topic=2759192
DKIM
https://support.google.com/a/answer/174124
As to your open rates, it depends. I've been doing email consultancy for the last 7 or 8 years and have seen everything from less than 1% to 100%. (The 100% was a double opt in Christmas advent calendar I did when I was working at Playboy UK, each day in December we sent people that had requested it, an advent girl. On Christmas day, it got 100% opens, but clearly that is far from normal).
Check out my email tips in the Education Series on this very board, there are three in the series. 101, 102, and, yes, you guessed it, 103. Hopefully there's some helpful info there.