It's an interesting thought experiment. The most favourable comparisons in terms of bomb load and crew (using the later Mosquito variants capable of carrying a 4,000lb bomb) are often made with the USAAF's B-17, which typically carried around 4,000lb of bombs on long-range missions with a crew of ten, rather than Bomber Command's mainstay, the Lancaster, which had a typical load of 14,000lb and a crew of seven. The Mosquito was cheaper than the Lancaster (around a third of the price), and had a lower loss rate (0.65% compared to 2.2%), so not too far off the sort of figures you sometimes see mentioned.

For the sake of simplicity, let's say the RAF wanted to replace its Lancasters with twice the number of Mosquitos, as that keeps the overall engine requirements identical (the Mosquito having two Merlin engines compared to the four of the Lancaster). As you say, the construction methods of the two aircraft are completely different, the Mosquito using pressed and glued wood rather than the metal of the Lancaster; I'm afraid I haven't got comparative figures on skills and training of workers that aren't factored in to the simple cost per airframe, or even whether the required raw materials would be available for a greatly increased production run of Mosquitos, but it certainly wouldn't be possible to simply switch one for the other, any such decisions would have had to be taken years earlier to avoid a massive delay in output. On the (rather large) assumption that production was possible, there would then have been a major issue with aircrew.

Two Mosquitos would need four crew, rather than the seven of a Lancaster, so that's a saving. Except you would need two pilots and two navigators for the former, as opposed to the Lancaster crew of a pilot, flight engineer, air bomber (bomb aimer), navigator, wireless operator, and two air gunners. As Bomber Command massively expanded, aircrew training was a serious bottleneck. During the inter-war years aircrew roles other than pilots had been generally neglected, and as the focus became four-engine heavy bombers with larger crews the need for a drastically scaled up training plan was clear. In late 1941 the situation was far from ideal, particularly at Operational Training Units (OTUs). These were the final stages of training before aircrew went to an active squadron, and ideally would use a similar type of aircraft (often slightly older models withdrawn from first line service), with instructors ideally consisting of experienced crew who had completed a flying tour. Lacking both, there was insufficient capacity at the OTUs for pilots coming out of initial training, and the crews entering squadron service were often unsatisfactory. At this time the policy was to have two pilots for large bombers; in early 1942 a single pilot policy was adopted, allowing training time to be increased without affecting the flow of pilots; formal categories for Navigators, Air Bombers, Wireless Operators, Flight Engineers and Air Gunners were established; and training plans restructured accordingly. It would have been an extremely heavy burden to try and produce twice the number of pilots and navigators for a larger force of Mosquitos, those roles needing longer training and more flying hours than e.g. gunners and engineers.

The Air Ministry certainly looked at the efficiency of its aircraft; a 1943 study covering June to September found the loss rate of the Lancaster, Halifax and Mosquito was 3.5%, 5.4% and 2.3% respectively; however with average bomb loads of 3.95 tons, 2.20 tons, and 0.68 tons over that time, the Mosquito came out below even the Halifax in terms of weight of bombs dropped per missing aircraft. An April 1944 study was more favourable, calculating that the Lancaster and Mosquito each 'cost' around 20 man months per ton of bombs dropped (compared to 60 for the Halifax). (Randall T. Wakelam, The Science of Bombing: Operational Research in RAF Bomber Command). It's fairly clear that, for sheer weight of ordnance, it wouldn't have been possible for the RAF to practically replace its four-engine heavies with Mosquitos, and if twice the number of Mosquitos were simply substituted for Lancasters it's another question as to whether their loss rate would have remained as low; of course the German reaction would have been different if confronted with a different threat. That leads to other arguments about Mosquitos being used differently, e.g. in precision daylight raids rather than area attacks by night, or other variations in Bomber Command's composition and tactics, but then more fundamental changes are firmly into /r/HistoryWhatIf/ territory.