Traditionally vinyl tiles are manufactured in such a way that when they are installed they are tight and square to each other with no gaps in.
Apliy vinyle seems.
Seal the seam with vinyl seam sealer.
Away from the seam to guide the applicator nozzle but don t get sealant on the straightedge.
How to fill gaps between vinyl floor tiles.
How to seam vinyl sheet flooring.
As for thread for sewing vinyl on most vinyl you can use general purpose thread but if you expect the seam will experience a bit of a stress use heavy duty thread.
Nylon is the best second best would be 100 polyester.
This product is designed to economically seal seams in sheet flooring and keep debris and water from collecting in seams.
Cover the seam with a transition strip.
Apply a bead of seam sealant over the seam.
Those holes will weaken the vinyl and make it prone to tearing.
Hold a straightedge about 1 4 in.
This non flammable solvent free vinyl sealer saves time and costs compared to heat welding on commercial vinyl applications.
How to seam vinyl flooring.