Hello @all.
I just wrote this as a comment under one post, but I felt like posting it might help new travelers find it as well.

So .... here we go again. With slight changes.
M(30) with GF(25), from Germany just for the record. 

To start. If you like hyper Party Environment or Tourist Souvenir Store after Souvenir Store roads, you probably wont find any infos afterwards because we personally do not enjoy those artificially constructed only for tourist things.

SIM: Esim, easy peasy. YeSim has good offers and we had good connection nearly everywhere. 30 days 20GB. 20€.
Do not know if smaller tarifs also habe the same provider. 

We did the route in approx. 3 weeks. The drive from Bacalar to the west takes 5-6 hours. The rest should be done in 2-3h each. 

We got our car at europcar in Playa del carmen. (~400€ for 21 days with all insurances, etc.)
Very easy and nice Service. No scam or hidden fee.
You can take a ADO bus from cancun airport  there 1h driving.
Some others might scam with hidden liability insurance. But never met someone who actually got scammed. Just read about it.

Since they had a major image campaign in the last years, the whole route is veeeery save. We even walked around every of those towns at night.
Do not know about every small town,  but we were never scared once in all days. But ofc. make your own experience and only fo Stunden you feel save with.

For money. We did Santander. ~60Pesos ATM Fee. Others are waaay more expensive for us, but ofc depends on your banking company. 
Be aware: A lot of ATMs are empty or out of order, so sometimes. It might take 2 or 3 attempts to find a working one.

Petrol stations sometimes try to only take Cash. We only payed with card and went to a different one. Ask beforehand. 
Always check that the price is reset before they start filling your tank. 

For card payment in General. Pay in Pesos not in your lokal currency. This makes it cheaper because you do not pay for conversion. Same for ATM! Always withdraw in Pesos!!!!

Bacalar is awesome. Can just reccomend the rectangular Pier at "Ecoparque Bacalar". Especially for sunrise (to see it over the lagoon) or sunset.

We did a sailing trip for 3h (700 Pesos). Yak Hostel is a good place, they have all trips and no scam prices. Also kayak,etc.

Driving to Campeche we slept in Xpujil to visit Calakmul Maya Ruins(very early. You should start at 6 a.m. .Park opens at 6 archeological site at 8, but you will need the time, because it is very far. The road is paved so easy driving. Do not go fast, because you scare the animals. You will habe a better experience if you go with the speed limit.
Search for "Zona Arqueológica de Calakmul" in google maps, otherwise might be hard to find. It is south-west of Xpujil. Be aware you drive 2h till you get there, but there are nearly nooooo people and you can climb up the 40m high ruins!!! Many animals. (We saw for example: Toucan, Boar, many monkeys even on top of the maya Ruin, that looked awesome, Eagles -> Harpy eagle, other exotic birds, foxes(wtf...) and some more i do not know the englisch words for.)

Westcoast is nice, but Keep in mind those are kolonialised spanish cities.

Campeche visit C.59 at the evening/night. Everybody sits at tables in the street,  you will definitely find an appeling place.

I enjoyed Merida more than Valadolid. So if you can choose stay there longer. Do a "Free walking tour" in the morning and ask them for the best things to do. Gives a nice start in the day and ask them for stuff to do.
Go to "Museum of Yucateca Gastronomy" at 3 p.m. to get to See how they make the iconic food Cochinita pibil the traditional way. You also get some for free to taste and can eat it there afterwards.
The whole area around this place is nice to explore by foot. For example oldest church at mainland in Merida and oldest building at Plaza Principal.

Also...obligatory advice. If you go to Chichén...Go at opening our. Otherwise very crowded. Main parking is 150 Pesos. You find parking infront for 100/50 Pesos and is also save! Then you just walk 2 minutes. Check for their signs. Do not take the first parking Spot you see. :)
But I have to be honest. After Calakmul, this one was also nice to, but the otherone was way more enjoyable cus we felt more like explorers. And is way cheaper and less crowded.

Tulum....I think it is overrated. Very expensive. Everything is privat. Party spots do not say "hey I am in Mexoco" at all. Could be anywhere in the world to be honest.
Tip: Ruins on sunday are 50% discounted for tourists as oftoday. Go to the parking "Estacionamento Oficial Tulum Mágico". This way is cheaper than entering though parque Jaguar. You can also drive with free shuttles once you are inside. No plastic bottles allowed. They check Bags. Also go early at opening hours and you might have the park for yourself. We were the first car 10 mins before opening.
Also: at the beach/hotel area you can go through every hotel or resort if you say you just want to go to the beach. They have to let you though by law, beaches must be public.
There is also a public access if you do not want to talk your way in. Parking there is 100-200pesos. We always got it for 100 after talking a bit.
Alternatively bicicle. 
Check out the plaza "Parque Museo de la Cultura Maya" there are often festivals or events in the evening/night.
La Pizzine TRIA hast live DJ, but is only open a few days the week. They have 2 other places in Tulum. Always DJ(sometimes starting a bit later 9/10pm) and a bit Party.

Dunno if someone is reading this, but I found it hard to get good reviews so I wrote alot.

Have fun! Please excuse typos cus of autocorrect. 

Let me know if it was helpfull in the comments. 
And enjoy the trips. Mexico is special but very enjoyable if you get used to it.

And ofc depends on how you like to travel....a lot of people love tulum for example! I just felt like it is only there for tourists.

And a three last words:
 1:Be carefull buying from advertising guys on the streets. Prices are most definitely to high and quality of product or trip is most of the time worse. 
2: Real Supermarcets are you best friend. Aki everywhere or La Comer in Tulum have better prices and a lot of offers compared OXXO or 7/11.
Buy Mezcal or Tequila, etc. there instead of Souvenir Shops!
We found stufd that costs round about 3-4x more in germany or souvenir Shops.
3: Buy local mosquito spray if you are not used to them. Orange packaging for spraying.

25 Day Trip Mexico - Personal experience Nov25