I converted a 44X70 machine shed with 2- 13'2" 20' doorsto a shop, for the same reasons you listed.  When we built the machine shed in 1972, 20' 13'2" clearance doors were the biggest that company offered in a farm building.  It worked OK, but there were some disadvantages.

One mistake I made was pouring the cement floor in the previous dirt floor machine shed.  I poured it in sections as I could afford it, and never dreamed of adding pex tubing later, as at that time everything was copper tubing in the floor, and few people did that on the farm, although a local dealer had it in the floor, as well as the grade school I attended.  I knew I wanted in-floor heat, but never figured I could afford it.

Other thing was the size of the doors, combine was limited as you mentioned, as well as folding out things.  Very unhandy.

Insulation in the walls was added in sections, first part I did was not insulated well, and it was too big a job to do over.

I found out too late into the project that the rafters were designed for an aluminum roof, which had started leaking a bit.  I could not add a ceiling and insulation due to the problems of weight support and not seeing a leaking roof.  I was able to patch the roof, but never knew when it would start leaking again if I had a dropped ceiling.

Plus, I need all the height I could get to open the door into the engine compartment of the combine.  Had to park the combine between rafters to even open the door to the engine while in the shop.

I heated the shop with a torpedo type diesel heater, really got a lot of fumes from winter projects, had to open the doors often.

I lacked the ability to put up bifold or roll-up doors, as I didn't have enough height to get equipment in, and those doors would provide problems.

I failed to put in drains, something very important in a shop where you bring in wet and snow-covered machinery to work on.

With all that said, my shop was in an excellent location, very handy to the house.  We had never had a place to work that was warm in the winter, and most of our neighbors were working out of even smaller buildings that basically held tools for work outside the door.  We considered ourselves lucky to have this shop, and kept adding to it over time, decreasing the one-time hit of building a shop in one year.

I'm not sure anyone can build a shop with everything they want in it, I would say most would want something different shortly after building it.  A shop is never high enough, never wide enough doors, never big enough, never has enough storage, etc, etc.

I always wanted a place to clean up equipment inside in bad weather, with drains and all, seemed equipment I wanted to work on needed cleaning often, but never planned for that.

Only you can decide what you want, no matter what you do, you will wish for something different later.

Reading between the lines of what you said, I bet you use the shed you have now for the shop, as I understand it is in the right space, and space for another is limited.  Farmers are smart, they almost always find a way to work out problems, you will figure it out.

No matter what you do, build a new shop or use the old, there will be something you want different after the project is completed.