Some tips from a fellow pack rat and hoarder.
First, plan your space. Decide on what the final layout will be. Plan for big tools to be on casters. Plan for cabinets up high on the wall. Use all available space up high and above the garage door. Plan yourself workstations that allow for a flow of work and materials. Once this is planned start with removal and reorganization:
Buy at least 3 big tarps.
Take everything out of the garage and put each item in one of 4 piles labeled:
Trash or recycle
Give away or donate
Storage
Put in it's place
The first two are self explanatory. The third is for items not needed in the garage shop and should be put in storage either in the basement or in another storage solution like an outside shed or storage box. The idea is to get everything OUT of the garage/shop that is not absolutely necessary for it's function.
Now you can throw away the trash items and take to recycle items to the recycle locations.
Immediately take the give away and donate items to their respective recipients.
Now take the storage items and put them in storage right away.
Next, following your plan from above, Finish or clean and refinish the ceiling, walls and floor of the garage/shop. Do any construction needed of walls, insulation, electrical, plumbing and HVAC. Install the storage solutions such as cabinets, shelving and etc.
Note: Everything you are going to put in the shop should have a place to be.
Now, place each item in it's predetermined place.
The result will be a workspace that is purpose driven with just the tools needed.
Don't be overwhelmed. If you want to break the job into smaller pieces, then do the sorting and disposal and storage steps first and you will have one much smaller pile of things left. This will be the pile of things going in to the shop/garage. You can now design the garage/shop around these things and your list of future acquisitions.
Easy peasy lemon squeezy!