Seem I would need the RGB mod done to use the OSSC which may well be the route to take. Thanks for the info!
No worries, OSSC can be quite an investment but useful for multiple systems.
The other thing to consider though is NTSC vs PAL region consoles. Quite a difference between the two in terms of different resolution and Hz output. Some mods can change the Hz output but I am not sure about the resolution signals.
If you want anything outside of a quick nostalgic fix and plan on playing retro games regularly via original hardware, I find PAL consoles a bit jarring compared to todays standards. NTSC is definitely the way to go if you can.
Personally I use a Framemeister with a NTSC N64 and the TW RGB mod. I can vouch for it being decent but don't expect miracles as the N64 does look a tad rough still! I've tried my PAL Mega Drive 2 and have not had the best results, image looks great upscaled but mine keeps cutting out and the sound is slightly messed up, something I'd like to look into at some point, might just be a dodgy cable or capacitor.
Retro Gaming Cables provide good quality cables and are considered one of the best in the business. I'd recommend checking those out. They sell the Rad 2x occasionally and are supposed to be really good, might provide a decent solution for your MD1.
My life in gaming YouTube channel can be a useful resource for retro gaming on modern displays. Well worth checking out if you're interested.
Outside of all of this there are plenty of decent emulators out there and Retro-bit sell decent replica Mega Drive controllers. Might be the best route if you want to keep costs down and avoid the faff

.
Edit: I forgot to add the Rad 2x might be a good option for playing on original hardware and keeping the cost down, if you plan on using a few consoles. The Nintendo one works across multiple consoles but the Sega and Sony ones are for particular consoles. From what I understand these are great upscallers and almost lag free. I'd consider this as a great option on original hardware as you wouldn't have to invest in multiple scart cables to use with an OSSC.
Second edit: If I get some time this week, I'll try and upload a comparison on the N64 between composite and RGB scart (with deblur and without) via the Framemeister. Might give you an idea on whether or not it is worth pursuing in the first place.