Go for it - that's a nice commute and there are lots of possible routes you can take.
In terms of training, Haringey still seem to be providing free cycle training for adults - website link below:
Lots more here .....
I was in the same boat, but started cycling to work a year ago and it's now absolutely my favourite part of the day and I'm kicking myself for not having done it ten years ago. I was intimidated by the thought of cycling in town (my commute is Turnpike Lane down to Bishopsgate, so went out on a few weekends just pootling round quiet streets early in the morning, and then went along for a bikeability course, which was really helpful. I also spoke with friends and colleagues who cycle, read lots of blogs/columns on urban cycling, and watched bits and bobs on youtube.
My commute is pretty much the 141 route, but I dodge some of the more daunting junctions (TPL and Old Street) by taking quieter back streets when I have the option. I've actually been very pleasantly surprised how accommodating and sensible 99% of motorists have been in my experience, and my policy is safety over speed, so I avoid practices like cutting up the inside of lorries and buses. My journey takes 25-35 minutes depending on traffic and weather, as opposed to regular journeys of up to 90 minutes when trying to get home at 6pm on the bus or a struggle on the tube.
I also got a mate who works and lives nearby to cycle to and from work for a week, which gave me a lot more confidence and gave me some great pointers on technique and positioning.
No specific advice on bikes, I'm afraid; nor with a route, but it's possible to have a ride through FP, pop up one of the roads that runs parallel with Blackstock Road, turn onto Brownswood Road, cut across Blackstock, wind round Gillespie Road, Drayton Park, get across the Holloway Road, head up Liverpool Road and then work your way through the backstreets until you come down to the bottom end of Cally. Just follow your nose, leave plenty of time and you'll settle on a route in time. When you're more confident, you can take a more direct route along busier roads. N. That might be a rubbish route suggestion, but that's the way I've done it in the past. This is a good starting point when plotting a route - http://london.cyclestreets.net/
Anyhow, congratulations on your decision - I'm sure you'll quickly learn to love it.
Just to say that I think this is a really good suggestion for an initial route to Kings Cross - I often go that way and it's pretty straightforward. The worst bit sadly is getting to Finsbury Park ... (which for me involves Wightman). A lot more about that on the other post that someone linked too earlier.
I'd suggest taking a left off Drayton Park onto Horsell Road just before you get to Holloway Road and crossing Holloway Rd. using the toucan next to the Cycle Surgery. Would also recommend going straight over Liverpool Rd. and down Westbourne, Thronhill, Barnsbury before heading west at some point.
If going to Bishopsgate I leave the 141 route at Ardleigh Rd, turning left at the end and then right at the roundabout. Heading down De Beauvoir Rd you can go through Hoxton market or continue down Pitfield Street.
I recommend cycle training to everyone.
It's worth checking if the council where you work offer free cycle training to people who work there even if they don't live there. Then you can double up, eg have some training now on safe good road technique, then once you've been commuting for a while have another session and focus on specific problems you are encountering or roads you don't feel confident with.
Apart from the confidence it's not going to be as big as jump as you think. If you know how to drive on London's roads, you know how to cycle on them. You might not be confident about that yet, but you do.
You may well be surprised just how much fun it is though :)
The closest descendant to the Miss Marple style sit up and beg today are Dutch bikes eg Gazelle or Batavus, but they are not that cheap and can be heavy. I love 'em but when I switched my commute from the City (6 miles mostly flat) to the West End, (7 miles, 2 noticeable hills) I switched to a lighter bike. There are also some newer British companies making bikes in the style of the seventies and eighties Raleighs like the old Caprice ( eg Bobbin bicycles) - would be a good choice but on the other hand an original from Ebay woudl be a lot cheaper.
If you have an old hyrbid knocking around I would get that serviced and fit it with mudguard, a rack and north road handlebars, possibly with a bit of a rise (height) to them. You'll end up with something with a roughly sit up and beg position for about £60, but with a much wider gear range. We did this to my BF's bike and he loves it, it's like riding around in an armchair! The idea is to get you up and running at minimal cost, then buy a new bike a few months/ a year in when you've got a much better idea of the type of thing you want.
If you haven't got a bike already, look for an old 3 speed Raleigh, Triumph etc on ebay, and take it to a bike shop to get it checked and serviced, or if you are a DIY bod just find some online tutorials, it's all very simple. They cost more than they used to but still a lot less than a new bike.
I have a Raleigh Clubman which I absolutely love to bits. Well worth finding out if your work are signed-up to a cycle to work scheme as that makes a dramatic difference to what you might be able to get for your budget.
& invest £10 on the best book to keep you out of danger: