Use Free Pascal?

Yep. That's what I'm gonna do.

I've been developing a program using both TP and FP, jumping from one to the other. I prefer working in TP better though; it's more of a habitual thing rather than a necessity.. I prefer compiling in FP, because the coded program runs faster.

1) Also, I didn't know about the unit heapex until after I wrote the initial message.. all this time I've been looking for memory leaks just using memavail (!) and FP doesn't have that...

2) also, another thing that prevented me from using FP entirely was the fact that the crt unit in FP is slow to output to the screen... so, instead I'm gonna try using the video unit. again, I didn't know of this unit until after I wrote the initial message...

so long as FP works in these two aspects then this message is pretty well moot...

although, I am still curious as to what is going on preventing me to compile in TP. But that's just a curiosity...

Don't know what's preventing compilation, but it's been said a lot here that DosBox is meant for games 😜.
The FP CRT unit works rather well for me, but I'm not compiling (why would I these days) DOS versions of my programs.
Isn't that unit supposed to be heaptrc?
As for IDE conveniences, if you haven't tried it, maybe you'd like to look at Lazarus, it manages CLI programs too.
The only thing I miss about TP is the debugger, the FP debugging facilities are...lacking, at least I haven't found a way to modify a string variable within the debugger (I can look at it at least ¬¬).

I recall having used borland pascal 7 in dosbox though, although that's ussually for very small test programs.