Hi,
I have a Siemens panel (I don't have the model number in front of me). I've read all the labels. It says its max rating is 125Amp, it had places for 24 full sized breakers, and the label states it supports max 48 circuits. The bus/bars in the panel all support 48 lines as well.

Does this mean that I could theoretically use tandem breakers in each location? How else could it reach 48 circuits? Currently there is only one tandem breaker in my panel.

I'm in the design phase of a huge basement renovation and I'm running out of circuits. I have 4 full size locations available for me to use in my basement (the washer, dryer and furnace are are other circuits).

I'm adding a jetted tub, so that's one circuit. I'm adding a lot of recessed/pot lighting, so that pretty much ties up another circuit. The bedroom will require an AFCI circuit, so that is another one tied up, and AFCI's are usually full size breakers. There are various GFCI requirements for the bathroom, and then all the other lighting and plug requirements... And I'm adding hydronic infloor heating, so I'm guessing that the pump for that system will likely require its own circuit as well.

I might... might be able to squeeze it all to the 4 full sized slots, but it would be extremely tight.
The reason I'm looking at the tandem breakers is because I do not what to upgrade to a larger panel or branch off to a sub panel. I am thinking I could replace one or two of the full sized 15A breakers with tandems.

Also, when I get the full electrical layout drawn up, can I post it for critic? This is by far the largest wiring project I have ever done, and this will be going through all inspections.

Thanks
Darren