I didnโt want to chime in because Iโm heavily involved in Animal Welfare.
It really depends on many factors.
##What type of traveller are you?
Here are some general answers:
###a) Youโre planning on just travelling within your own country:
If youโre venturing on a road trip or moving city to city then itโs not so bad. Cats can handle being moved around a relative amount but like @wanderingdev says, theyโre territorial and they can get lost easily within the first few weeks if theyโre outdoor cats - so just be aware.
###b) You are planning on being an expat.
If youโre looking to settle down for extensive periods of time (years, preferably) then I approve of taking your pets rather than leaving them.
###c) Youโre changing countries constantly.
Not good. Quarantine, vaccinations, stress of flying/long distance travel on a regular basis is not good for a pet - 6 months is too often. Lots of pets die from flying every year. Be careful how much stress you put on him.
Second cat
Introducing a second cat to a home can be extremely stressful. Like said before, cats are territorial. To introduce a second cat to a home requires at least 3 weeks of restraining the second cat to a room and building up the scent/contact. Itโs laborious and takes forever. Whenever someone wants to adopt or foster a second cat, we have to explain in detail the best approach. Itโs not for the faint hearted and itโs not recommended to put your cat under stress before you subject him to travel (secondary stressor).
I also disapprove of you wanting a second pet because youโre too busy to exercise/entertain him. It seems like your lifestyle is not suited for a pet at this time. If you want to travel and you donโt have time to play, the best thing you can do is rehome him to a household who have time for him. We all make sacrifices for our pets: yours should be to either play more and travel less (frequently) or rehome him to a better suited household.