Looking for gear & accessories advice

I have recently got into astrophotography and use a stock Canon 7D mark II with 400mm f/5.6 and 50mm f/1.8 II. My circumstances don't let me spend more than 2/2.5 hours out photographing hence the amount of total exposure time I can manage is limited.

Till now I have only managed around an hour of data couple of times (https://astrob.in/full/strjmh/0/ & https://astrob.in/z8xjyc/0/).

I believe the following can help me gather more data in the limited time I got. I am looking to photograph DSO in the range of 50mm to 300mm.
1. HA mod of my DSLR / or get a used HA mod DSLR (if second option, any suggestions?)
2. Get a used f/2.8 lens which gives reasonable results at f/2.8 (I don't pixel peep, so bit a of coma is fine in the corners). Thinking of two lenses... 24-70 f/2.8 & 70-200 f/2.8, zooms because I will be able to use them in day time photography as well. Any recommendations? Have heard good stuff about the old Tampon 70-200 f/2.8.
3. Is the Red-dot finder helpful? Finding the object quickly can be very helpful considering the limited time I get. Any views on this one - https://www.widescreen-centre.co.uk/omegon-red-dot-finder-for-dslr-flash-shoe.html?
4. Any other suggestions?

Thanks in advance.

- Rudy.