i've actually been working on something similar lately.

i have been usinb blockbench for 3d modelling. it's easy to use, and makes lowpoly models that can somewhat fit the n64 style

the inset image is the actual 3d model in blockbench, pretty much directly inspired by the bully enemies from mario64.

the scene that takes up the bulk of that image is that model in unreal engine, in an unlit scene with faked vertex-based goraud shading on the materials. the goraud shading is what hides the sharp lines of the polygons in n64 games. you can find ripped n64 models online, and if you look at them in modern lighted rendering, the polys are sharp, but on the n64 they have that softened look from the goraud (and in a few later games, phong) shading.

generally speaking, the n64 used max of 64x64 px textures, tho several textures in mario 64 are actually 16x16 and 32x32. there were some tricks used in some later games to render larger textures, like the clock on the clock town tower in majora's mask. the other thing about n64 textures was they were rendered with a unique three-point bilinear filter. in my opinion it is almost indistinguishable to the eye from regular bilinear filtering.

as for finding assets that look like n64 assets, that's been tough for me to find. there is alot more indie nostalgia around the PS1 style than the n64, and more assets around that mimic the style of the former. alot of what you will find is the modern 'mobile style' low poly stuff, which doesnt really capture the feel of the oldies-but-goodies.

there are some good youtube videos that explain and break down how n64 graphics worked better than i ever could:

https://www.youtube.com/watch?v=vskDAr8_8bU&t=7s

https://www.youtube.com/watch?v=8qb6B3WwbPI&t=508s

https://www.youtube.com/watch?v=LJHPaKskvd4

generally speaking, modern 3d rendering engines need some extra tricks to get the old look and feel.