So, I'm a little lost.
How much free memory fastbasic provides ?
Booting the FastBasic 3.5 atr disk, loading FBI.com, entering PRINT FRE() in the editor, then pressing CTRL-R to parse/compile/execute shows 30755 after that tiny bit of code. When compiling as an executable to disk, the FRE() amount will be less (around 2K less or so) bc of the inclusion of the runtime. Using FB.COM the above sample will yield about 29467.
dsmc has done a fantastic job with his BASIC.
Yes, in the IDE you have about 31200 bytes free at the start, this will be used by the program source (in the editor) and the compiled code.
But, if you compile the program to disk (pressing CONTROL-W on the ide) you have about 37600 bytes free, because you don't have the compiler, editor and source in memory, only your program code and runtime.
And finally, if you compile with the cross compiler (from a PC), you will have more free memory because the cross compiler includes only the parts of the runtime that are used.