Welcome to the group. Trans flush : normal mainteneance. Motor sound when using the brakes: normal, thats just the pump working. New CV (rebuild the oem ones, dont buy aftermarket): not a big deal, normal for IFS vehicles. Check engine light and traction control lights on: could be a big deal or could be nothing. Go to Autozone or Oreilly and have them read and give you the codes then post back here.
As for Monteros, people are probably gonna get mad at me but imo they are not very reliable if your definition of reliable is not requiring a lot of maintenance. If your definition of reliable is that they last a long time with maintenance then they are very reliable but in that case, a lot of things are.
Monteros have plenty of items that need way more maintenance than most vehicles because of a lot of design drawbacks/flaws and these expenses are compounded by them by very finicky/particular with what brand of parts can be used and a limited service and support network.
Imo - you’ll spend way more money maintaining a Montero then say an Explorer but an Explorer would be a much worse platform for building up for offroading.
What are you looking to do with your rig? If it’s just for daily driving then there might be a lot of other better options because Monteros don’t command/hold their value as well as many other more popular vehicles.
That’s my opinion after having owned around 2 dozen vehicles in my life, 4 being Monteros. That said, they’re my favorite vehicles for overlanding/camping/exploring and if yours is rust free and want to sell just let me know, I could use a low milage one (seriously)!