Just a couple of thoughts from me, promise:
Get the longest length slider your space + budget allows, regardless of new or used or with / without special features. I think Hammer machines and other Asian imports are decent for the money and would be a huge step up from the old school cab saw. The Felder line has a premium that it's made in Austria, with, yes, a nicer slider, but is it's not worth *that* much more that the equiv. lower tier models.?
There's always another tool to buy, so don't over think it and remember the "why you got into this hobby" probably wasn't based on tools / brand / etc. It seems you have a budget constraint, so as a young woodworker, you'll have a chance to upgrade once you get further along.?
Sang Luu