I usually make 30 to 80 Tracks per Song. But I usually have to freeze on my single machine (PC see specs in tagline).
after 10 Tracks, to be able to work. Do I need slave machines or how is it possible to work without the need of the freeze function or bouncing? And what does it take to work on the hardware side? I’ve heard there are even projects with 300 or more and those people don’t even seam to freeze any of those tracks. 
Can this even be done with a single machine?
There are so many variable. Are you running at 44.1 K or 96: or higher? I am running at 44.1 k. I am working on a track now about 100 tracks (not counting groups) … Over 20 virtual instruments, fully loaded mastering chain, automation… no freezing. Several NI Guitar Rigs etc. I have a Universal Audio doing the most of the reverbs and delays so that helps. I am using RME like you (raydats in my case). I run a Hexicore i73 3930K rig overclocked to 4.5 ghz on water cooling.
But there are some virtual instruments that just munch the processor. I think it depends on how you work… I am running this current session at 512 samples during the mixing stage to get more asio headroom.
I’m working only on 96k, using lots of FX on many virtual instruments. Nothing external (all in the box).
I’ am really curious on what it takes (if possible in these times yet) to work without latency issues (including to widen the buffer and risking not to be able to re-track audio tracks properly without the use of freezing again). 
Agreed. 30-80 tracks without freezing is no problem at all on my machine BUT if they’re all running CPU heavy VSTi’s like Serum for example then forget it. Specs are in my sig.
I very rarely freeze stuff and my projects are usually over 100 tracks when they’re finished but again, it totally depends exactly what you are doing in the plugin department.
It also depends whether you need to run at low latencies. I’m not too fussed about that because once a project is at an advanced (large) stage, i’m usually mixing and not recording (and also can use my Steinberg MR816CSX if I need to do low latency recording).
I wonder now: How many ‘heavy ones’ can you use without freezing in your constellation?
It’s impossible to give a reliable answer because it varies depending on how many tracks are playing at once, whether you are using a very complex preset in a VSTi synth, how much polyphony you are using, whether you are using lots of complex group routing etc etc etc.
But just to give you an example, the project I have open now has 119 audio/Instrument tracks plus 16 groups and 16 FX tracks. It’s running about 125 plugins, channel EQ on most tracks, plus the following VSTi’s with no freezing:
14 x Sylenth
12 x Serum
5 x Kontakt
3 x Spire
2 x Gladiator
1 x Massive
ASIO meter is at about 75% Average Load, 25% Real Time Peak although that’s not a very good guide really in my experience. I’d say there’s quite a bit of CPU juice left in the tank.
Just for the hell of it, I added a load more Serum tracks to the above mentioned session and I got to 82 before it started to break up. That’s on top of all the other VSTi’s/plugins described above, so a total of 107 VSTi’s.
Most of those serums are playing quite a simple preset though, with only one note of polyphony.
Well working in 96k you would have approximately half the resources to play with.
Try running at 48k and decide if the extra resources are worth it after mixing down and comparing the end results.
Yep, it’s debatable whether 96k is worth it but that’s a personal decision. No way I’d work at 96k if the trade off is freezing tracks after I have 10 VSTi’s running.
I work at 44.1 seeing as the delivery format for pretty much everything I do ends up being 44.1 anyway.
If the tradeoff is reduced audio resolution for more layering and texture the 96K loses the quality battle hands downs. Most people don’t listen to bits they listen to music. In a perfect world wouldn’t have to choose both life isn’t perfect.