At what point in your campaign do the players decide they

[Shorty Lickens]

need a base, army, corporation, town, fortress, or ultra-tank?

Is it when they've been going for years, have acquired vast wealth and respect and possibly land, and they don't know how to spend it?
Or is it early on, when they want to make a small home base out of nothing or someone else's derelict building?
Did they start with a tent? or a broken down old shop? or maybe their preference was an abandoned warehouse? Or possible the ruins of a small village that nobody has the guts to take back?

Did they ever end up managing a company? or private army? or town? Did it get attacked? Did their people ever turn against them?

More than once I've heard guys say they wanna start a new campaign by being small business owners and it was tough to get started. Theres some material across the Rifts books but not a whole lot. And a merc company, even a small one, need severe funding just to get off the ground.

OR, do they sometimes decide they need a space craft, and get the idea they'll start exploring the galaxy?

[taalismn]

Usually they start looking for a base/real estate when they've acquired more loot than they can easily carry around and don't want to sell off("Part with my collection of power armor?! NEVAH!")

[Shorty Lickens]

SUB-QUESTION!

Lets say your plucky band of misfits ends up in a run down old ware house they intend to call home. Where do they begin? Do they set up beds, a kitchen, automated defenses? I guess it might depend on who your characters are. If you got a bunch of Operators I'm guessing they will want a work shop, so they can build automated defenses, so they can do other stuff and not worry.
Techno-Wizards obviously have different procedures, though I bet they too will eventually want a work shop, and automated defenses.
Shifters probably have all kinds of crazy ideas for an abandoned warehouse, especially if its anywhere near a ley line.
Juicers will likely set up a basketball court.
And of course Crazies need a vegetable juicer and ping-pong table.

[taalismn]

Secure the premises first...check structural integrity and points of access and the best places to watch them. Is anybody(like local hobos) or anything already living here? Decide which entrances can be closed off permanently or need to be reinforced. What's the best place to sleep with regards to security, comfort(heating, power, water, dampness, etc.) and, if we have to, can be escaped from easily? What needs to be addressed NOW, like a leaking roof, swamp in the basement, or sparking bare electrical wires? Can we turn on lights and heat the place openly, or do we have to stealth the place so as to hide our presence here? Or at least reduce the perceived amount of activity inside? Can we hide vehicles inside?
Can we tap existing power or do we have to bring in our own power sources? Likewise water and other utilities. Can we use an existing sewage system or do we have to use chamber pots or an outhouse latrine?
Can we build safe rooms/fortifications inside? Can we lay down traps/wards?
Can the place be expanded on, or subdivided to meet specific needs? Can we get in materials to reinforce it? And how much of our resources are we budgeting for the work?

Once a place is secured, and at least an internal campsite selected, facilities allocated, then a good cleaning up is in order to evict and dissuade vermin from living in the place. Then start rebuilding at leisure.

[Warshield73]

It really depends on the group. Most of my groups never make it that far, prefering to rent lockers from Operators or other such businesses in secure cities like Lazlo, Merc Town or Kingsdale. Anotehr group started talking about a base in the second adventure when they were attacking an enemies base. They kind of decided it might be a good one for them.

My original group started with the locker rental in cities (by the end most of the had forged documents, weapons, cash and vehicles in a dozen places on 3 continents and two alternate dimensions) but as they went on each PC had their own base in a different place. In this base all the other PCs left equipment and had at least basic access.

As for setting it up, it usual went:
1) Set up defensive positions to repel attacks
2) Escape routes. Usually at least 2 and they could be tunnels or mystic portals or some sort of fast get away vehicle like a jet.
3) Basic need. Food, water, basic shelter and power
4) Automated defense. Auto Turrets and the like with a mix of tech and magic. Tectonic entitles or magic constructs with armor and weapons were a favorite. Also mine fields and drone robots like Dyna bots
5) Secure storage. Vaults and ammo bunkers.
6) Advanced Defenses like shields, heavy weapons and missile batteries
7) Last step and it went on till the end adding amenities - Luxurious quarters, a brig, repair and medical facilities, swimming pool and gym, even additional defenses