If I understand correctly, you have decided to purchase instruments thru the installer and the installer is recommending that you not purchase the 2 instrument displays to save money both on the purchase and the installation? That's not a bad thought but I would recommend that you purchase the navpod that provides enough space for the chartplotter and 2 instruments even if you don't buy the instruments now. I agree with Dave that you don't really want your displays to be limited behind the helm. It is very important to have instrument displays visible from anywhere in the cockpit. But I would install the autohelm control at the helm.
I have pictures of my before and after condition. I bought the boat with a 7" chartplotter mounted underneath the instrument displays. These displays were the older set dedicated to speed, depth & wind. Admittedly, I went overboard with my new installation because I bought a 12" chartplotter where a 9" would probably be more suitable. That said I also installed a new pedestal guard, which necessitated installing the chartplotter at the higher location. It looks very obstructive and top heavy but in practice, it functions well without being obstructive to my field of view (it helps that I'm 6'0"). I also desired to have engine controls on the pedestal at a functional height, so that is what is mounted under the chartplotter. There was a lot more behind these decisions that I care not to elaborate on.
I didn't want my bulkheads cluttered with anything because they make marvelous backrests (I removed those disgusting line pockets) and I had to get creative where to mount 2 instrument displays. I bought a stainless steel handhold that spans the companionway opening and mounted a navpod for 2 instruments. Sorry I don't have a better picture without the lantern in the way. The base of the handhold was very close to the exact opening width but I had to make 2 bases to secure the mounting pads. My installation isn't elegant. The cables exit the back of the navpod and are secured to the back side of the handhold so that you don't see them. I had to drill a hole in the deck to feed the cables into the cabin. The cables come out in the galley ceiling and from there I routed them as discreetly as possible under the glass holder and to the space over the nav station where my NMEA 200 back bone is routed. I hid the cables with teak trim as best I could. It's not a professional looking job but it is effective and I absolutely love, love, love my instrument displays over the companionway. With the c-clamps, the angle of view is adjustable for best viewing. The handhold is a nice addition in its own right when climbing into the cabin with additional security. It is low enough it doesn't block any view. It hasn't restricted any space when climbing into the cabin (that was my biggest concern). And it fits just inside the dodger. I used a Scanstrut cable seal on the deck and it is under the dodger anyway, so water doesn't penetrate.
This is what I had when we bought the boat. Your pedestal is probably the same and this shows a 7" cp. If I were you, I would install a navpod large enough to mount the cp and 2 displays so you have room for addition. You can buy the one that does not have pre-cut openings and only cut them out when you ultimately decide what else you want to mount. I would mount it on the lower angled section and leave the upper vertical section bare.
Here is my only picture of the displays over the companionway. Sorry about the lantern in the way. The 2 instrument displays are very, very useful and you will be missing out if you don't mount them somewhere visible in the cockpit. But you can always add them later, after you decide the best location. I posted another picture that shows how top heavy my navpod for 12" cp and and 2 displays look. Functionally, I love it. Aesthetically, I'm not that happy. When I bought the new pedestal guard, I was surprised by its configuration (the new ones changed dimensions - long story) and it left me no other option than to mount it this way.