Alright... my first post here and it's because I have a major backyard problem.

I left for 2 mos on a clinical rotation and I had someone watch my house while I was away. I come back and my back yard is irreversibly overrun with weeds 1-2ft tall.... It's a 4582 sq ft yard.

I planned on redoing the yard and planting grass next year when I could afford it. Now that my yard is a hazard and the ugliest yard I've seen in my entire life, I'm prompted to take immediate action.

Alright so here is what I planned on doing to clear and restart anew and plant grass:
Plan 1
1. Week 1: Remove all weeds (big ones by hand, small ones by mower), take out old plantar boxes, break up concrete slabs from old 50s yard compactor. Rent out a roll dump and toss all of it in.
2. Week 2-8: Solarize Yard (I live in CO, so I heard this may be the most effective way to get rid of 2-4" of superficial weed, seed, etc.) **
3. Week 9: Dig trenches, install new irrigation, Bring in enough fill dirt to cover yard. Plant grass seed.

My Questions:
1. My yard isn't very level. After I remove all the superficial weeds by hand and by mower, should I bring in fill dirt regrade/level my entire yard first before I solarize it? Or should I solarize my yard first, then overlap everything with new fill soil?
2. The cost to cover my entire yard with 4mm polyethylene clear plastic rolls is going to be around $160. What's the difference between 2mm vs 4mm in terms of effectiveness? Would it be cheaper, faster and more effective to just pull all the weeds out, spray everything with roundup and then overlap everything with new fill soil, and then plant grass seed by week 5ish?
3. I also want to install my irrigation system, or at least the piping for it ASAP. Should I do this before I solarize, that way I don't disturb or exhume deeper weed seed later when I dig trenches?

Plan 2:
1. Week 1: Remove all weeds (big ones by hand, small ones by mower), take out old plantar boxes, break up concrete slabs from old 50s yard compactor. Rent out a roll dump and toss all of it in.
2. Week 2: Dig trenches, install irrigation system with all piping, Backfill/Regrade/Level Yard with new top soil
3. Week 2-8: Solarize entire yard to kill the remaining seeds, weeds just underneath the new top soil
3. Week 9: Plant new grass seed.

So Plan 1 OR Plan 2 OR A different plan...

Please help, trying to get my yard fixed before winter and if I plant grass seed according to these plans, it would be the 1st week of September when I plant the grass seed (Blend of Tall Fescue). It'll give me 6-8wks of growth before potential for snow fall (CO It's inconsistent, could have the 1st snowfall in October, or later, typically the whether stays around 50+ degrees though up til Nov, with periods of colder days.

Thanks