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Sounds like you're going to want something bigger, it's just a case of taking time off work and spending money on a course then the gear and the bike + insurance. If you've got a few grand to spare should be no problem.
When I did it time was tight and money too, doing them separately and putting up with a small bike for a few months helped to spread the cost. If you have a permanent job and a family, giving up the time/money to do it can be an issue. Great to get the full licence though and well worth the price of entry.
I guess you're thinking about the motorway part of the journey and keeping up with cars. You can't ride on a motorway with L plates anyway (which you'll need if you only have a CBT). Try taking an alternative A road it would be more fun anyway.
T junction safety is one of the big problem areas of motorbikes and where you need to worry most, getting overtaken by cars in almost any scenario doesn't pose a huge risk as you're not that big an obstacle. It doesn't happen very often anyway.
Maybe try a 5 day course where you go from no license to fully licensed.