Use the best tool for the job. If your trading style isn't limited by Excel and VBA why switch? Finance is basically just one giant spreadsheet. To be honest, I mostly program as a means to collate data. My stuff isn't anything an Excel sheet and a little elbow grease couldn't do. In fact I mostly prefer to use Excel.
Migrate the chunks you need out of Excel. If you pick up C# you can write addons to help you offload stuff to "outside the sheet" in something a little lower level than VBA.
Again, Excel is absolutely fine. Work around it until you absolute can't/won't - then look for something else. Python has it's own problems - dynamic typing means you don't have an IDE that can discover types and 15,000 lines later you'll look back and wonder what you're even passing in. Believe me, I work professionally in Python and have written a handful of Python projects around finance. It is a great language to replace Perl as a prototyping language but it is absolute garbage for anything at scale (for a more practical example - look at the problem dropbox is having and how they've basically had to hack type annotations and type checking onto Python in order to continue to use it).
EDIT:
To address your question on VBA directly - it will not dramatically improve the speed of your sheet. It is better than using formulas but you're still using Excel as a VM. If speed is a concern considering writing Excel addons to do what you need or offload data processing/collating to a language better suited for it and only load in the refined data into Excel for final processing/study.
That's the whole point of Python, to speed up development. Type hints work fine and if you want to enforce them then compile with Cython. I know, I know, "it's not python" but it might as well be.
Excel is far too unstable for any serious work. I used IB's ActiveX many years ago and it froze a few times and the code was often broken after a new API version. The GUI mixed with code is a big mess and it was very cumbersome.
Python isn't too slow for any kind of trading you'll do on a retail account. I run my stuff from a VPS that's in NYC while connecting to IB's Chicago servers and even then my cumbersome code it's fast.
On top of that you can develop on Windows and run the code on Linux. Windows for an automated trading machine is a very poor decision and should be avoided. You'll also enjoy avoiding platform fees if you're a cheapskate like me.