Hi KPgardens! A lot going on, sounds like.

1. The rain garden is at least 10 feet away from the house, right? Scratch that - you had water in the basement, so your NEW rule is 15 feet away from the house.

2. So this area is already wet, plus a new sump pump will also outlet here? If so, a couple of things. First, do an infiltration test here, to see what soils you have. Clay? If so, this will be a very wet rain garden. Second, make sure there is a safe overflow. It looks like the overflow would be over the walkway? That is not horrible, but in the winter, it would create ice, especially with sump pump water. You might consider piping the sump pump water under the path, and making the rain garden beyond the path.

A sump pump garden is a little trickier than a typical rain garden. It needs a good overflow, and is generally wetter. So adjust accordingly.

How big is that space? You have a drain line, installing a sump pump line, utility lines and an invisible fence in there. Before anything else, you must get the diggers hotline out there to mark the area up. Once that area is marked with everything, spray paint in those lines. Take another photo from the same perspective as the one in the OP. It may make you think twice about planting in that space. Or what you can or can't plant. Roots can become a problem.

@Susan Bryan Thanks for the early feedback! We expect the sump will never turn on at all...Maybe once every 10 .years. It's truly an emergency sump, so crossing fingers. But if it did - it's not likely happening in the winter, so we're okay with overflow over the walkway. there is no way to relocate the rain garden to the other side of the path given our needs for yard use (dogs and more). Net: I don't expect this to be a sump pump garden, but city code required me to do this...or cut a drainage path and connect to the city rain sewer. Now I'm wondering if I'm making a mistake by choosing .garden. ?? That said - we do get tons of runnoff from the neighbor's driveway into our yard (it'd downhill from them) and I think a thirsty space to soak up any of those events would be super handy.

@beesneeds The space we will install will either be ~150 sq ft or 300 sq ft depending on what we optimize for. But we're doing to do the infiltration test to be more specific about our needs now that ground has thawed. As for the diggers hotline - we've already done it a million times there, and will do it again before hand digging: the only big concern I have is the ATT fiber line. All the rest is easy. I'll put another few photos in here of this area in my yard. More to come - thank you all! Also thrilled to have @Susan Bryan visiting next month. :)

Shows the downward slope from driveway to my garden beds & lawn (and the underground french drainage line to street). A lot of that sheds to my yard during rain, but some of it obviously sheds to the street.

This is a 6yr old picture of what we trenched in ~6yrs ago to eliminate water pressure on the side of my house. drains to green grate & stones in my sidewalk garden bed. It's deeper than we'd be digging for rain garden, but it's likely the most centered bit of underground stuff we have to ensure we don't damage.

Wow! Beautiful plan!

Ok - I get it. Since you don't expect sump pump water to go here, where you placed it should be fine. :)

It looks like the overflow of the rain garden would go into another bed - nearer the sidewakl. That sounds fine. Now that I see the plan, I understand more where it is going.

Looks good! Keep going!