In my experience you need to plant significant amount of peas to get sufficient harvest. Choose earlier maturing varieties if your summer season is short and you want to succession plant, or if your spring season is short. I like planting peas almost everywhere and especially where I intend to plant heavy feeder warm season crops.
It's important to track position of the sun. Especially further north, the sun's angle and where it rises and sets in the sky will make significant changes in available sun exposure for your garden over the course of the year.
For me, peas do best where it will be sunnier during the shorter days but NOT the sunniest area where it gets too hot once the days start getting longer in May and early June. This causes them to fry faster when we have the occasional early heat wave. By planting in different locations, you will have the advantage of different micro-climates and extend their harvest.
I pre-germinate most big seeds in the house to get a jump on the season -- it takes 2 to 3 weeks for them to sprout outside. I've documented most of what I did this year in the seed starting forum -- you might find the information useful.
I have found that some of my beds get NO SUN AT ALL in the winter and also become shaded earlier on in the fall even though it seemed like a sunny spot. This also means the area remains in the shade of something -- trees, house, etc. -- during the spring thaw when overwintered crops like garlic will start to wake up, and ground will remain colder and not thaw or dry out as quickly so you can start planting.
When the shadow is created by trees with leaves that don't fall until later, or by a solid structure like one of the surrounding houses, the garlic doesn't seem to grow as well. It's also important that the area is not in a low or cold spot where snow drifts are heavier and the ground remains wet and soggy, though extra high mounded rows or raised beds in those areas will alleviate the situation. I have been in search of ideal garlic planting beds but not all of mine will grow them well.
When you are succession planting, you don't always have to wait until (all of) the previous crop is harvested. Leave a little extra space with mature plants in mind, and you can plant the new seedlings or sow (pre-germinated) seeds in between. Harvest a hole in the lettuce bed and pop in a seedling, etc.
You might still be able to start some of the cold hardy non-heading crops like lettuce, Asian greens, cilantro, etc. if you give them some protection. Walla Walla onion is supposed to be able to overwinter, though it might be a little late -- I think they were supposed to have been started in August. I'm still going to start some now though, just to see if they will survive. But based on previous experiences, I have pick a spot where I can be diligent about keeping them weed-free.