Suggestions for a new bike for a newbie
Congratulations on the 50 miles and deciding to get back into the sport.

An 'adventure' bike is probably a good choice for getting back on a bike if you want a road style bike (i.e. one with drop handlebars) that can take on some rough road surfaces and is comfortable to ride.

The characteristics you want to look for are:


More relaxed riding position (compared to road racing bikes)
Tire width 28 - 32mm
Disc brakes
'Compact' (50/34 tooth chainrings) or subcompact (48/32) drivetrain.


Adventure bikes have a lot in common with cyclocross bikes but are not quite the same. Cyclocross bikes tend to have more aggressive riding position and often a single chainring. 

All the large manufactures have adventure bikes in their ranges. The budget you mention will get you solid alloy framed bike. You should definitely spend some time looking around at different bikes and do lots of test rides.