Did you purchase 1/2 or do you own the entire building? If you own the whole thing, matching doors would be a good start.

We purchased the whole building, yes. Matching doors will be done for sure!

While I love trees - yours are not worth saving as they were planted much too close to the house. Remove the trees, then repost so we can see a "full frontal" view.

Have you had the shingles etc. sampled and tested for asbestos? Because if it were mine I wouldn't do any remodeling until this had been done first.

A realtor that showed me a 1920s cottage (that he had not visited in person before) pointed out similar looking shingles as soon as we were walking up to the entrance, said they were asbestos.

My current house was approved in 1979 and still there is asbestos. As in 20% asbestos floor covering in most rooms (a dangerous amount is considered to be 1% asbestos or more).

The asbestos service provider I have had do a few things here bought a 1920s house for himself and removed the popcorn ceiling, because it was asbestos.

Remove the trees by the house. They will otherwise wreak havoc on the foundation.

If it were me, I'd prolly go super fun with color because the exterior doesn't look exceptionally remarkable. Quirky may increase the rent!

Houzz has some great color ideas in the articles. See these examples (there are many):

Choosing color with just 2 cans of paint

18 exteriors

Unexpected color schemes

One home, 5 colors

Is one side of the duplex to be your residence or is this intended as a rental investment?

If you are keeping it as a duplex, two matching doors is a great idea.

Add a full width 6' deep covered porch and full width front steps with a 6' deep full width ground level concrete slab landing ... all divided by a center railing.

Then outline the sidewalk with bricks or pavers buried so only their tops are exposed.

Consider creating a small private patio area on each side of the entry box for each tenant -- not concrete but a mix of pavers with grass in between them ... easily mowed.

https://www.houzz.com/photos/outdoor-fire-pit-with-concrete-grass-pavers-modern-patio-orange-county-phvw-vp~20847724

You might consider beginning a green privacy hedge in front of the landing slab (leaving an opening at the sidewalk, of course) to add more privacy for the patio for each renter -- could be a good selling point for some. Consider a shrub (w/o briars) that keeps its leaves and looks good year round that will grow well in that geographic location. Would Aucuba bushes grow in your planting zone?

Agree with another comment that painting all the exterior siding on the entire structure one color with one trim color would be a good idea. If the upstairs siding is still in good shape, consider using that neutral color and all white trim. Paint the downspouts that same color.

While I like trees in the yard, I agree with a prior post: those trees are too close to the foundation.

Would remove all the landscaping man made "things" -- those white border / outline pieces for the planting areas, etc. -- and focus, at least initially, on creating the perfect lawn all around the structure.

If those are Forsythias (shrubs with yellow blooms), keep them but consider trimming them at the appropriate time to create a more dense shrub -- check out care instructions on line.

You might consider moving any and all shrubs planted against the building away from the building and planting them elsewhere.