Are there modern tools to make retro games easier these days?

You could use drawing tablets and trackers back when, indeed many would have. Just cost a lot more to get it all in the first place. Modern software is also a bit less crash happy and inclined to autosave. True pixel art within console constraints is a bit harder as most people favour the aesthetic rather than the constraints* but there are still a few things.

As far as making it easy. Not really. Some proof of concept compilers have been made for high level languages on the 16 bit stuff but going much beyond text adventure, slideshow, visual novel or the like is not going to happen. You might just about have a library for mod playback but as you will be implementing it in assembly then how much that saves you (and how much it handicaps you if the hardware exceeds MOD/XM/whatever's basic parameters) is a different matter. There are some nicer assemblers I guess but it is not like labels and comments were hard back when and there are only so many shortcuts/macros you can really do. You will still then be learning assembly for old and limited processors and the attendant hardware layouts/functionality.
Back on expense then a max size as it would have been back in the day cartridge is usually nothing drastic to do or assume your emulator/flash cart users have trivially (modern PC won't care that you have an 8 megabyte ROM and most flash carts these days support SDHC which starts at 4 gigs). Some of the custom stuff cooked up to expand resources in a massive way (see that SNES video streaming thing) might get a bit more fun though.


*choice video

 

Can't say I, even as a hardware or bust ROM hacker, get the fetish for restricting yourself to old hardware for homebrew purposes but to each their own.

Does not seem that tough. Most things have reasonable homebrew designs for flash carts ( https://web.archive.org/web/20070623024735/http://www.reinerziegler.de/ )

Making a page/bank selection protocol is not very hard; there are a few things you can use to talk to the cart, or these days sticking a little microcontroller in there to respond accordingly to a certain pattern of (potentially illegal or just never happen in normal operation) requests.
Kick one of those to either more storage beyond what any imagined for the original stuff (though you might have the fun of handling or restrictions of main loop having to be in the always visible window) or results of your audio chip, graphics chip, control inputs if you are expanding the functionality and yeah.

Getting support for it on emulators is the hard part as you would have made yet another custom/HK/pirate mapper.

 

Most music trackers have been open-sourced or reverse engineered and have been ported to windows or linux. If I were you i'd start with something simple like Fasttracker 2 or Impulse Tracker, however OpenMPT supports both of these and might be a better pick if you dislike either's UI. You will have to keep original hardware implementations in mind however, modules with high amounts of channels (think 16-32 and above) take a lot of CPU power to playback.

 

Depends on how far back you want to go. For GBA I think there are some tools to make life easier but anything older will be quite lacking in anything resembling modern tools. You could always try your hand at ROM hacking, it's easier than making something from scratch. Super Mario World romhacks have been done to exhaustion yet I am still constantly amazed at the things people manage to make with them these days.
Many retro games have pretty good ROM hacking tools made for them already but if you want something unique nobody else has be prepared to learn some assembly to make it happen.

 

NESMaker?

 

GB Studio may be something worth looking into for you, it's a drag and drop game creator that can create GB/GBC games and requires very little actual programming knowledge. You can import your own assets, including sprites and music created by separate programs so if, for example, you wanted to use a drawing tablet/pixel art creator for your sprites and backgrounds you could totally do that.

The current stable version only supports standard GB style (so black and white, essentially) and just jRPG games, however there's a beta out right now for GB Studio 2.0 that will let you create GBC games and adds functions to support other genres like point and clicks, platformers, and I think shoot em ups now, too. Whether or not they can truly "stress" the hardware in the way you're referring I couldn't say, but it's certainly worth a shot if you just don't know anything about game dev/programming.

 

Film (and other long form video).
Internet seems full of examples of this one -- I certainly watch hours of video a day sometimes from people messing around in their garage with gear that costs not a lot. You might have to play to your strengths (if you have a phone then filming at night gets harder, as do massive zooms, however do it in daylight or with a nice bright light and all good).
Some of them have other skills and maybe some loaner gear from work but plenty do not.
You have plenty of examples of low budget stuff going back decades as well and made on a shoestring with a handful of people.

Games. Fair few people have done some very impressive stuff with unity and unreal engines, and how many games from the pros do that too?
Also while you somewhat dismissed it above this also says nothing of the looks retro but at the time would have been "yeah we might see an arcade machine do that in 10 years" or "yeah you can do it, for one sprite on a plain background with no music and nothing else happening on the whole game" (see a lot of the demoscene) option which any number of people have used to great effect over the years to make things still talked about/known today where so many efforts in said unreal and unity engines are barely remembered even by those that played them.

You can do the old hardware thing if you want but 99% of the time anybody doing that is doing it to teach themselves low level coding, electronics (the line between digital logic and low level coding gets rather blurry, and indeed most of the best coders I see doing this sort of thing come from an electrical engineering background more than straight coding or physics). If you want to do art (be it music, graphics, animations and the like) a la 8 and 16 bit then go for it, many have a great time making such things just like they might have a good time mimicking any other art style. However jumping in with serious/hard restrictions in palette, tile size restrictions, memory restrictions governing object count, maybe animation restrictions and all the rest (which often enough newer systems gained more and more to eliminate or render as small as possible ( http://pineight.com/gba/managing-sprite-vram.txt )

Videos