Hello Community

I got ten days for Colombia in my one month trip and will be arriving by plane to Cartagena from Venezuela. For what I have read, I should at least spend 3 days there, but after that, I have no clue. My objective is to visit a friend in Ecuador so I have to go south and in some way cross the border.
Which takes me to my first big question, is it that dangerous to cross to border on te south to Ecuador??? For what I have read around, so it seems, but I wonder if there are safer places than others where to do it, or if I should really fly in from Cali or so. I am really down to earth traveler so comfortable to go on local transport of pretty much anykind. I talk spanish too, and have kind of a latin american accent since I am from canary islands, spain, and due to heavy migration to latin america till the 80's, my culture and language are very similar. Still, I dont want to get myself into trouble. Definitely not the plan of tis trip

I also havent found anywhere how long (kms or hours) could the trip be from Cartagena to Ecuador, which I guess it would have to go though the main cities. Anyone knows??? I have calculated around 1200 - 1500 kms but might be totally wrong

If that is so, I guess 2 days max by bus would make it, meaning I would have another 4-5 to stop on the way down south to the border. I also really like driving but also havent heard if it is expensive to rent a car or dangerous to drive around, or pay-offs to local authorities for being a tourist :-) Feedback on this issue would be great too.
In this sense, I am looking for advice too on where to stop, worth seeing or doing, and I guess a bit exceptional, cause it seems Colombia is wonderful all over. I am open cause I will also have another ten days in Ecuador for whatever I havent done, so in this sense, I am open to beach (fiesta and diving) or mountain (skiing or canooing or mountain sports) or even city, although not so much this last one. Seeing something exceptional like a desert or so wouldnt be bad neither. So any comments on this would be greatly appreciated.
Wow, I am so excited about this trip. Colomba will be my second stop. I will be coming from a week adventure in the Canaima National Park to see the Angel Falls, highest waterfalls on earth. Can't wait for all this to start

Thanks in advance. There seems to be lots of great people with great experiences here so can't wait to hear what you guys think

Fito