[Selur]

Why don't you apply any IVTC of pulldown or deinterlace of any sort? The DVD source is awful.

That were just example calls.
For the trigun example I used:

# Imports
import vapoursynth as vs
import os
import sys
# getting Vapoursynth core
core = vs.core
# Import scripts folder
scriptPath = 'i:/Hybrid/64bit/vsscripts'
sys.path.insert(0, os.path.abspath(scriptPath))
# Loading Plugins
core.std.LoadPlugin(path="i:/Hybrid/64bit/vsfilters/GrainFilter/RemoveGrain/RemoveGrainVS.dll")
core.std.LoadPlugin(path="i:/Hybrid/64bit/vsfilters/Support/fmtconv.dll")
core.std.LoadPlugin(path="i:/Hybrid/64bit/vsfilters/DeinterlaceFilter/TIVTC/libtivtc.dll")
core.std.LoadPlugin(path="i:/Hybrid/64bit/vsfilters/SourceFilter/LSmashSource/vslsmashsource.dll")
# Import scripts
import mvsfunc
import havsfunc
# source: 'C:\Users\Selur\Desktop\VTS_01_7.mkv'
# current color space: YUV420P8, bit depth: 8, resolution: 720x480, fps: 29.97, color matrix: 470bg, yuv luminance scale: limited, scanorder: telecine
# Loading C:\Users\Selur\Desktop\VTS_01_7.mkv using LWLibavSource
clip = core.lsmas.LWLibavSource(source="C:/Users/Selur/Desktop/VTS_01_7.mkv", format="YUV420P8", cache=0, prefer_hw=0)
# Setting color matrix to 470bg.
clip = core.std.SetFrameProps(clip, _Matrix=5)
clip = clip if not core.text.FrameProps(clip,'_Transfer') else core.std.SetFrameProps(clip, _Transfer=5)
clip = clip if not core.text.FrameProps(clip,'_Primaries') else core.std.SetFrameProps(clip, _Primaries=5)
# Setting color range to TV (limited) range.
clip = core.std.SetFrameProp(clip=clip, prop="_ColorRange", intval=1)
# making sure frame rate is set to 29.970
clip = core.std.AssumeFPS(clip=clip, fpsnum=30000, fpsden=1001)
clip2clip = clip
# Deinterlacing using TIVTC
clip = core.tivtc.TFM(clip=clip, clip2=clip2clip)
clip = core.tivtc.TDecimate(clip=clip)# new fps: 23.976
# make sure content is preceived as frame based
clip = core.std.SetFieldBased(clip, 0)
# cropping the video to 700x480
clip = core.std.CropRel(clip=clip, left=16, right=4, top=0, bottom=0)
clip = havsfunc.DeHalo_alpha(clip)
clip = core.resize.Bicubic(clip, range_in_s="limited", range_s="full")
# Setting color range to PC (full) range.
clip = core.std.SetFrameProp(clip=clip, prop="_ColorRange", intval=0)
# adjusting color space from YUV420P8 to RGB24 for vsVSGAN
clip = core.resize.Bicubic(clip=clip, format=vs.RGB24, matrix_in_s="470bg", range_s="full")
# resizing using VSGAN
from vsgan import ESRGAN
vsgan = ESRGAN(clip=clip,device="cuda")
model = "I:/Hybrid/64bit/vsgan_models/2x_LD-Anime_Skr_v1.0.pth"
vsgan.load(model)
vsgan.apply() # 1400x960
clip = vsgan.clip
# resizing 1400x960 to 720x556
clip = core.resize.Bicubic(clip, range_in_s="full", range_s="limited")
# Setting color range to TV (limited) range.
clip = core.std.SetFrameProp(clip=clip, prop="_ColorRange", intval=1)
# adjusting resizing
clip = core.fmtc.resample(clip=clip, w=720, h=556, kernel="lanczos", interlaced=False, interlacedd=False)
# adjusting output color from: RGB48 to YUV420P10 for x265Model
clip = core.resize.Bicubic(clip=clip, format=vs.YUV420P10, matrix_s="470bg", range_s="limited", dither_type="error_diffusion")
# set output frame rate to 23.976fps
clip = core.std.AssumeFPS(clip=clip, fpsnum=24000, fpsden=1001)
# Output
clip.set_output()

Can you please tell me the differences between the upscaling types and what can support CUDA?

Nowadys VSGAN should tile the content if need be, depending on the model setting an overlap would be recommended.
At least for me the VRAM usage doesn't seem to change in regard to the vs threads.