My answers in italics
I was using one of my grandfather's old Minolta's. The light meter in it has proved tricky for me to use, so any under/over exposure is likely.
I think your image os properly exposed
I do the developing myself. I used D76 at 18C for 9 minutes. I'm not sure, I know the "ideal" temperture is around 20C/68F but I have no ways of heating my chemicals, do chemical temperatures have any affect on how the negatives will turn out looking?
Development is temp sensitive, warmer developer will act faster and colder slower.
Check in the Ilford website for a time-temp adjustment chart.
http://www.ilfordphoto.com/applications/download.asp?n=430
I have to admit that I do love high contrast and am used to high contrast situations.
I was considering pushing the HP5 for more contrast. I'll try that next.
You may try that yes, but I think your next idea is better
I will also look into some colored filters. I currently have a UV and a polarizer. Could the polarizer help at all in this situation? I've read that they can enhance things sometimes, but have not done any experimenting.
Polarizer would have probably not helped you in an overcast day.
Use it to darken sky or to make reflections in glass or water less noticeable, it is a very useful filter, but it is too easy to over-use it
A yellow or orange filter would be far more useful for BW photography
Considering the film, I use HP5+ for a few reasons: I generally love the look it gives in most situations, this one being an exception - I'm wondering if it's the film or just me, or a combination of both. I'm new to the chemical side of photography, and HP5 has been easiest and managable for me to do, HP5 is relatively cheap and easy for me to get at my local camera store.
Your image looks very good for HP5+ in an overcast day, you may just have to learn some post processing
Any other films I could consider?
As of now, keep shooting HP5, and learn the quirks of it. Stick to D76/Id11 (they are the same)
After you are satisfied that you can squeeze some good pics from HP5 move on, I'd reccomend FP4 which is slower or Fuji Neopan 400