By the way i noticed that when i open 7 or more instances at the same time
Quite a bad start already. Remember the request limit imposed by BetFair. By opening 7 instances simultaneously, you should set the Connection Monitor in each to limit the number of requests to 20/7 = 2 per second! There is no way the software can do anything useful with that limit, therefore you're well above the limit if you're refreshing at least one market in each.
it opens an error message saying "Unable to start the logging system. Please change the logger port number in your settings and restart MF pro" as in attachment. I click in the ok botton and it opens the instance normally. Should i do anything? Or as that instance seems to work normally i can act as something not mandatory?
This error message indicates that the program can't record your logs. If you don't need them, you shouldn't worry about it, but if you do, I don't think that changing the port will improve the situation, as it is clearly related to too many instances of MF Pro opened at the same time. Not sure, maybe your system is somehow configured to prevent too many servers (MF Pro log server) started at the same time.
I wonder if there are a limit in the number of instances i can use at the same time in a PC or if the limitation is just the capacity of the PC (CPU and Ram memory mainly).
There is no limit in MF Pro, but just try opening 7 instances of Internet Explorer, each having several Betfair market pages refreshed, and measure your CPU load.
I also notice that without internet i can´t run the simulations. Am i making any requests to the betfair´s API while running the simulations?
When I got to this point, I actually realised you were talking about running MF Pro in Time Machine mode. OK, then forget about the BF request limit, it is irrelevant in this case, but the program still needs the Internet to connect to Betfair to request their authorization to use the API. Time Machine is operating under the BetFair historical licence, so they are still interested in who is using their data. That's why you won't be able to log in if you're offline.
But if you're running MF Pro in Time Machine mode, please bear in mind the load on your CPU is much heavier than when the program is operating in real time mode, because a database and a DB server are involved in getting the prices, and additional effort is made to decrypt the data on the fly and convert them into a readable format.
I hardly can run three Time Machines on my PC at the same time, and even then the fastest mode is missing a lot of refreshes because the CPU just can't cope.