I think a liberty ship makes a fine starter. I also think an LST would be pretty good too as long as you can think lightweight. A C3 platform based vessel is good too. The German Altmark is nice.
Liberty ship, T2 tanker, Mehoshi Maru (plans available in the Resources area), Hog Islanders, tramp steamers, and just about any other cargo vessel between 2-4 feet LOA should work well. Just stay away from the more specialist vessels like passenger liners, Milchkuh/Deutschlands, barges, destroyer conversions, etc.
Beginner? LST - Hands down. double rudder. 2P2R turns on a dime. simple shape (for Rosie the Riveter to make.) can be built in a weekend from scratch. then can be simple or detailed on top.
True, but a convoy ship is an excellent way to learn the basics of building and ship handling. Not to mention they are a much cheaper learning curve. At a regional event one could always come up with a fun little scenario. Did it in Statesboro. Lots of fun.
HMAS/HMS Albatross - built as an Australian seaplane carrier in the 1930s, used as a repair ship by the Royal Navy in WWII. About the size of a Liberty ship, bulged hull, tug-like superstructure that starts aft at the break of the forecastle, and flat forecastle with 3 cranes, but no superstructure. Two prop shafts, one rudder. There were 4" guns on the 2 forecastle sponsons and 2 on the aft superstructure. (If not used as a convoy ship Albatross is a Class 1 combat ship.) If you want to see what the ship looked like there are lots of photos on-line and the Navis/Neptun site has a 360 degree view of their 1/1250 model. The first Albatross hull made from my mold in 2008, and one of Ralph Coles' Indefatigable hulls behind it: Top and bottom views: This is the only mold I didn't sell. If you want a hull let me know.
Most likely gonna go with building a liberty ship myself. Just gonna need to find a place to do the work.
Here's an odd-ball that can be used as a convoy ship: HMS Vindictive, a victim of Washington Treaty restrictions on British heavy cruiser tonnage, 'demoted' to a cadet training ship in the 1930s and used in almost identical appearance in WWII as a fleet repair ship. LOA 605', beam 65'. (I hope to have the Hawkins Class heavy cruiser hulls in production by late September.)