I'm approaching this posting as someone with over 30 years of hands on experience of Morgans. It's practical experience stemming from the chassis up rebuilds of several Morgans including a 1971 4/4 and a 1968 Plus 4. (I'm currently rebuilding a 1955 Plus 4 4 seat Drop Head Coupe) and there's 5 more waiting in the wings.
Practical experience means just that - hands on and not just something I've read or seen on YouTube.
Both the 4/4 and the Plus 4 have their own quirks.
The 4/4 in its 1600 Competition form is probably the better of the two for a novice Morganeer and a few mods such as a 5 speed gearbox conversion increases its versatility. Ford Kent engine is both sturdy and tunable at a price. It shares its Salisbury 7HA axle with the Plus 4. Don't rule out the later CVH engined cars nor the Fiat engined cars for that matter
The Plus 4 is more of a drivers car and does take a bit more getting used to. The Moss gearbox, although very robust and tolerant of abuse does take a bit of getting used to. No synchro on first gear catches folk out. Particular Plus 4 quirks are the Elektron bellhousing between gearbox and engine and it's problematic clutch sleeve. Billy and Jack Bellinger can rebuild a Moss box to better than new and much of their mods are race proven in the cars they look after.
It's true that the Moss box can be rebuilt at home with the only special tool required being a 12" length of 1" dowling! Some spares can be culled from similar but not identical Jaguar Moss gearboxes though. Service parts are readily available from your local bearing factors (to avoid the Morgan markup that most dealers charge)
The Salisbury 7HA axle is a fairly strong and long lived unit. Until a few years ago, crown wheels and pinions for the earlier imperial axles were difficult/impossible to find but Billy Bellinger has had spares made.
Body work for both the 4/4 and Plus 4 is now a problem, with both Vic Champness (Black Phey) and Richard Williams enjoying their well earned retirements, it's not clear who will taken on the mantle of building body frames for Plus 4's and 4/4's.
Sheet metal work is well catered for and specialists such as Steve Barnes at Vintage Sheet Metal can help though you do need to be realistic about the costs of repanelling a crusty 4/4 or Plus 4.
The Drop Head Coupes, although stunning, are a money pit - a look though my invoices tells me a new panelled bodyframe for my 1955 DHC has cost me about £9000.
Instruments for the late 60's to late 70's cars are hard to find so make sure they work as they should - I've only ever seen 1 set on the open market in 30 years and the asking price was eye watering!
I'd steer clear of the earlier Series 2 cars even if they have been re-engined with either a Ford pre-crossflow or crossflow engine. This is on the basis that the early Salusbury 6HA axle fitted to those cars is inherently weak and spares are non existent!
Happy to assist further by personal message or by phone
Arwyn