Mac- ideally a desktop that won't be moving around and potentially getting lost/damaged/stolen. I'd absolutely NOT put them all on a mobile device like an iPad which can be lost, easily stolen, dropped & destroyed, etc. See mobile devices as relatively precarious devices while an anchored desktop is likely much more secure. If money is tight, you can use an older Mac for this. If storage is small on Mac, you can store these photos on cheap (third party) external storage.
If the photos have no natural groupings (home, work, personal, business, etc), import all into the Photos app on a Mac. If there are natural groupings such as personal vs. work photos, consider creating 2+ libraries in Photos to store each type vs. mixing them all together into one big pool. For example, I have a friend in Real Estate who uses a library for RE photos, another for business documents and a third for family photos. They could have all this in one giant library but this results in 3 smaller libraries. It's easy to switch between libraries in Photos.
If you want to put various groupings together, create albums in Photos and drag and drop favorites into those albums. For example, if there are- say- 500 photos in that 1TB library that are your favorites, create a Favorites album, drag and drop those 500 into it and sync that to your iDevices. No limit on albums- make however many you want.
Sync favorite albums to iDevices while leaving the bulk of the library you don't have to have with you back on the Mac.
If you think you have to have access to every photo you've ever shot at all times, invest in a NAS device like Synology to create & run your own cloud and store them all in that rent-free cloud. No iCloud (and its forever rent) required.
AND/OR, buy yourself maybe a 2TB portable drive to store all photos on that device to carry with you. Connect it to your iDevice when you need access to photos not synced.
AND/OR, sign on for forever rent with something like iCloud and store them all there. There are convenience benefits of injecting Apple between you and your media collection but you are also trusting for-profit strangers in the cloud to be caretakers of your media... and iCloud (and all clouds with huge numbers of users) is a very attractive target for hackers who are likely always working on ways to find their way into it.
Take your iDevices with you, shoot new photos or video and when you get back to home base, connect it to the Mac, import them into the Photos library, process them into your albums, sync again with device if any synced albums added new photos and you are ready to go again. I also suggest breaking out videos from Photos and storing them separately, tagged and then indexed with the TV app (or iTunes on an older Mac) and thus easily accessible via home sharing on all other devices in the home including- optionally- AppleTVs.
If these photos are all very precious to you, consider buying a BD burner and a bunch of blanks to burn the whole collection to optical for one more relatively compact backup archive. Store the stack somewhere very secure. Add to it as you add a significant number of new photos by burning another disc. When you buy 25 or 50 such discs, they come on a spool which can then be the perfect place to store a stack of them after they are burned.
If this collection is so large because you are a selfie-maniac, it's much easier to use a Mac to review 80 of almost identical selfie shots to find the one "perfect" one and then quickly prune the other 79 copies. Take time to prune near duplicates and eventually you'll have just all "best of" (selfie) shots. I've seen this MANY times, except the person just has a gigantic library because they don't do any pruning. 50-70 of what is basically the same photo is very likely a LOT of wasted space for no benefit at all. Prune! Prune! Prune!
Do the same with ripped music collections (organized in Music or iTunes), video collections (organized in the TV app or iTunes), etc. In those you can also make album-like "playlists" and then sync just those playlists to your iDevice. Mac can hold entire collections but take a subset of favorites with you synched to your iDevice.
Lastly, use Time Machine, Carbon Copy Cloner and/or Super Duper to back up your Mac, ideally to at least TWO drives with one fresh backup stored offsite and regularly rotating with the onsite drive. Why? In flood-fire-theft scenarios, a backup drive sitting right next to a Mac is likely to also be lost. But that one drive stored offsite will help you recover nearly everything.
This approach will allow you to spend far less on iDevices by not paying Apple's huge premiums on all that storage.
I think a 2TB iPad is only iPad Pro and the 2TB option adds about $1K to the price. Use much less than that to buy yourself perhaps a Mac Mini and then you can get a smaller storage iPad since you'll be storing your whole libraries on Mac instead of iPad. Also, since the Mac may then be doing the heavier lifting, you may NOT need to pay way up for iPad Pro and could instead get an Air or just the basic iPad. That would provide more cost savings to put towards that Mac or just pocket it.
