You can use cork (either as a glue down tile or as a click together floor) to work nicely with the wood without competing with it. Cork is technically wood so it works well with other wood products but it is often "non-directional" in pattern so you don't have to worry about a clash of wood grain, etc. Cork can be the fast, cheap way to get a nice warm floor without paying thousands of dollars for in-floor radiant heat. Just a thought.

Laying the new floor in the same direction as the old floor is not the normal way to go about this. In the building industry, it is more common to see layers that are staggered or "bricked". In other words if layer #1 is laid in a North-South direction, then layer #2 (the top layer) is laid perpendicular to it in an East-West presentation. If you want to run the new flooring in the same direction as the old, you will want to use some underlayment (plywood) over top of the old floor so that you can maintain the "staggered" or "bricked" layering system. That is one way to maintain the North-South presentation. Please work with hardwood flooring professionals who have some experience renovating these old gems. They will have seen what worked....and what didn't. Their experience will be invaluable on a project like yours.

Those "gaps" are mild. They are normal. They are expected. They tell the story that they are original. They are meant to be there. The new floors will eventually do that too...which means they will match (eventually). It might take a decade...but it will happen. And don't forget that once everything is sanded down, you will be VERY surprised at how those "gaps" seem to go away (visually). Why, you ask? Because some of that is dirt. Once the floor has been sanded down (1-2mm of wood is taken off with the sanding), the dark material between the planks gets shaved off as well. And voila...they look cleaner (because they are). Relax about the absolutely normal spacing between planks. Unless you have museum quality climate control, this LITTLE bit of shrinkage is normal and to be expected with every floor (especially if it is 30 years old).

I think you take a box of each and lay them out next to yours with your lighting etc so you have a true visual of how they will blend or contrast and to ensure the tones coordinate well. I would get up to 4 options at 1st to work with starting with the closest match to the furthest contrast that you like. Once you have them played out in the patter next to your floors and in your light and the scale of the space it will make a big difference. You will be able time step back and see if from afar, in different times of day etc. Some will stand out right away as the wrong choice, others will take a news days and fighting to decide and narrow it down. Just make sure you can take them back and any time limits for refunds. Try one out at a time. Hope that helps. I also take a picture of things when I first do them and sometimes it helps me pick out changes needed right away. Maybe that is just me but for some reason it is a huge help lol.