Absolute newbie - r36s style device

Seen quite a few adverts for the gamelab device with 15k games pre installed for £40. A bit of research later and I find its a clone of the r36s which from what ive seen run a better OS and run the games better, little bit cheaper at around £28 but would need an SD card with the games so price wise gonna work out around the same?

Read its hit and miss if you get a good clone and most people advise to replace the SD card.

My questions are:

Im not tech illiterate, I like to dabble with tech and have flashed OS to usb previously but can't say ive ever really used SD cards, what do I need to write onto them?

Looking at playing upto N64 games if possible, does this make a difference in what i should be looking at? What can these devices play up to?

I like the vertical style of the r36s but should I go for the r36s, r36xx or r36s+?

While the gamelab version comes with the SD card pre I stalled where can I get the download to create my own SD?

What size SD would you recommend? Is there a separate SD for the OS?

After all this considered what would be the price difference compared to the gameslab £40 clone and the advantages gained?