Arashi and Furashi are the same guy, or at least related.
After the Science Patrol and Ultraman finished off the first wave of Earth monsters, the Science Patrol was reformed into the Ultra Guard to deal with alien threats after the Zetton incident. Arashi quickly rose through the ranks and became part of the Japanese branch. His last name was changed perhaps due to a marriage, or other incident.
Chaos, a corrupting, mutagenic presence from who knows where, unrelenting, and will bring the doom of all sentient life if it wins? Hmmmmmm....
Iron King, titular character from the series of the same name, was created from Ultra DNA.
With all the recent Ultramen visiting Earth to defend it from monsters/invaders, it's no stretch that the government would want to create a similar hero for themselves to combat some of the terrorist organizations seen in the series. Iron King was created using the DNA abstracted from an Ultra while on Earth (Possibly Ultraseven due to their similar appearance) with Goro Kirishima chosen to assume the mantle. After the various groups throughout the show were defeated, and with aliens and monsters in the hands of the current Ultraman, the project was disbanded, with Goro and Gentaro retiring, and one marrying Tenko like the finale implied.
Glenfire was born from fragments of the original Fireman.
At the end of Fireman
, the titular character dies after an alien ship he was carrying explodes. However, fragments of Fireman formed in space, giving birth to Glenfire.
Besides, Gudon, Gammas and Twintail all appear in the series, so they're already connected somehow.