Plenty of advice has been given on websites, in books and on this forum about switching between openings, for example between the Caro-Kann and Sicilian. While not ideal, this is clearly manageable.
However, I have seen much less about switching entire opening complexes - especially from 1.e4 to 1.d4 (since in general, 1.Nf3 and 1.c4 can be more tailored to learning systems rather than opening theory, or at least I feel that the theory is less important), and since this is the situation I now find myself in, I felt it would be good to start a thread and seek advice on this.
As I've said elsewhere, the mainstay of my repertoire will be the Veresov, covering the 1...Nf6 and 1...d5 responses (except for 1...Nf6 followed by 2...d6/c5/various other weaker replies). Of course, this leaves the Dutch, 1...c5 and various setups (English Defence etc) to learn to, and of course these are completely different in nature to 1.e4 openings.
My original plan had been 2.e4 against 1...c5, but learning open sicilians renders half the concept of my switching to 1.d4 pointless. Therefore 2.dxc5 or 2.d5 are the ways to go I'm sure, but playing 2.d5 would mean that I would be creating extra work in learning the benoni complex (schmidt/modern), even though I believe these to be ultimately good for white. Therefore, 2.dxc5 is likely to be the way to go - are there any texts on this line? It seems to me that white should be able to prove some sort of edge with good play.
1...f5 is a different beast. 2.Qd3 is likely to be my choice, since I feel that the g4 pawn sacs are quite strong. But there's something to be said for the more positional crushes as well - there's just so many promising lines! (Only kidding, MNb

) There shouldn't be too much theory on 2.Qd3, and the only thing which worries me is that it was recommended in one of the SOS books, therefore probably bringing it to the attention of even the less booked-up players.
1...Nc6 2.e4 is the Nimzowitsch Defence, which I'm happy with. Although 2.c4 e6 3.a3 looks quite strong too (and, indeed, did for me the last time I played 1...Nc6). I'm not sure here either.
Then there's 1...b6/1...e6/1...d6/1...c6/1...b5 and the even sillier replies. In general, I'd back myself to be okay without knowing too much, most can be met by 2.e4/2.Nc3 following the same sort of plan.
The main question is, where do I start? Do I just play 1.d4 in my next game, learn the Veresov through playing it and if so, which of the other lines should I concentrate on first? Or, do I continue playing 1.e4 until the end of the season, then use the May-Sept break to learn these lines and test them in offhand games? (The problem with this being that there are a number of congresses in the summer with Monmouth/Stroud/Hereford/British Championship all being on my agenda)
Also, has anyone gone through this sort of major transformation before? If so, how were your results affected? Generally I score decently with white and I don't want to go on a season-long losing streak for no reason...
Cheers,
Craig