Tiagra rear derailleur and Deore crankset + derailleur compatibility
You problem comes with bottom bracket width and very likely chainline. The Author Ronin has a 68mm BB shell. With the Tiagra crank it uses a 'Road' type Hollowtech external bearing BB. If you fitted a Deore crank, which has a longer axle, you would need a 'Mountain' type Hollowtech BB with spacers. Without checking I don't know if the Deore crank has a wider chainline, but I suspect it does.

I think you are right you would need a MTB front derailleur, as the rings would be further outboard, but I strongly suspect there is a difference in actuation ratios between Shimano road and mountain front derailleurs which means the derailleur would not be compatible with the Tiagra road shifter.

With all the Road/MTB compatibility headaches,  I'd look at options for getting a lower gear ratio with a road crank. The popularity of gravel riding and adventure bike packing on drop bar road style bikes has spawned several 'sub-compact' cranksets. FSA currently makes a 46/30 crank which would get you under 1:1 with the 11-34 cassette.