ADVISE ON BEST WAY OF STORING A VEHICLE?

I wouldn't follow that procedure unless I was storing the car for at least a year or more, and I KNEW I wasn't even going to try starting it.

For you, I think that if you can drive a car even a few times a year, you can just try to keep the tank full, keep sta-bil in the tank (if you know you will be storing it for a couple months without driving), keep the battery either disconnected or on a trickle charger, and that should be enough. If you end up with a very special car that you don't want to drive at all, or won't drive for a year or two, then I would do the above procedure.

When you do drive the cars, try to give them a good 20+ minute drive. You want the oil to go above 210 degrees so that the condensation will boil off and evaporate instead of being circulated in your engine. Oil lasts a long time these days and syntetic has a good additive package in it, so I wouldn't worry about changing oil anymore than just once a year or every 5k miles or so (and that is a VERY conservative number, you could go much longer and much more miles without even thinking of it, but that number is very conservative).

 

Hi Gustan. I remember seeing some pics of the cars. Many thanks for posting them. I'm at the same place as you, but on a much much lower level.
This is what I do. Hope it's helpful
General
Do NOT even start the car unless you can warm it up and give it a run for a while (liked SRT Mike's advice). Having a guy do some work and moving 3 cars to do work on one car aint gonna cut it. You're always gonna have problems. Don't move the Diablo or LP to get to the Testarossa because you want to tint the windows. Tint the windows when the TR is at its time of use. (see 'organization' below
Once cars are started check around, listen for noises etc. Once you're ready to go out on the road (not until water temp has been raised to normal) go real easy. You've just awaken a slumbering machine. Think of how you want to be woken in the morning. Thrown out of bed and into your car to go to work? Or massaged into the day? Once up to temperature, wind it out. I hit redline in my cars all the time they are used once up to proper operating temperature. Use the brakes, suspension. Use the car.
Fuel.
I do not know about adding full or emptying tanks for storage. I keep mine very low. If fuel breaks down, I have a smaller amount to worry about than if it were a full tank. I don't know about gas stabilyzers. They seemed like a good idea, but I heard/read some things so I don't use them. So far, so good (10 years plus)
Organization
Turn this into a science/business. Park/arrange the cars so that they get rotational use. One season one set of cars gets used, another season another etc etc. I don't think it will work well if you want to use all 30 in a few months. These things are insanely temperamental. and would love to break if given the chance. Set up a white board or even a binder of when each car was started so you know instead of what you might think or feel the last time it was used. If you want to do some non imperative work (cosmetics for example) wait until that car gets its turn of use. Keep a list of stuff you want done to which car, so when it gets its turn, it gets worked on and you don't forget something when it's time to start using another car.
Battery maintenance.
I use a Battery MINDer on my cars. I like the technology and they have a way that you can run a parallel series off of one unit to charge up to I think 6 or so batteries.
Tire maintenance
Flat spots. I get them if I don't move my cars around. What I normally do is push them 6-8 inches one way or the other (no starting, don't even get in the car. Just set a small chock under the tires) every other month or so. I leave the e-brake off on the non automatic cars. Just chock them. As for over or underinflating them. I just bring them up to normal pressure, and add a little during the winter months as the air condenses.

Don't want to write more than what I did, so ask me or PM if you have any questions. In disclosure. I don't have any Italian cars. The other day after starting my car after sitting for over a year (no one say anything, I know I know) I told myself 'I could never have done that if it were an F-car or Lambo.
This might not be the way you'd like to use the cars, but I've found that given my lifestyle, this is what works for me in keeping these cars working as long as possible. And to add, I'm a pack rat like you when it comes to cars. I keep (and intend to keep forever) whatever I buy.

 

for a hard-wired battery tender, Moss Motors (www.mossmotors.com) sells one for $55 that you permanently mount under the hood so that all you have to do is 'plug it in'.

It is certainly easier than removing batteries or attaching them incorrectly.