Hi Team
I took up triathlon from a marathon running background and recently completed an Ironman. These tips may be interesting:
* Work rate on the bike is comparatively lower than on the run. For me, med paced running = c.160bpm heart rate, med paced biking = c.130bpm. Obviously different for everyone, but you get the idea. "Drafting" or following another bike very closely, drops my heart rate another 10bpm or so.
* Hill climbing on bike offers massive potential for hard work out, but places knees under considerable strain
* Recommend you stick with mountain bike - I still love riding mine, which is half the battle because you want to ride it. I trained a lot on the mountain bike - it's heavy so requires more work to propel. It also pulls good wheelies!
* Tri-suits are flashy, but not necessary - they also have minimal padding where you need it most. Spend the cash on a crash helmet and cut down gloves
* Cycle at a cadance rate of about 90 revs per minute for max efficiency. Use the gears to control effort and speed
* Take a drink on the bike and a spare tube / levers / pump. It's no fun pushing the bike home 5 miles in the rain!
* Yes, get the World's brightest jacket - I recommend the yellow and black ONCE team jacket which you can get for about £40. Reduced near misses from about 3 per trip to almost none for me.
Enjoy that bike - it's a great way to stay fit and build strength.
As for the swim, it's great for CV fitness and overall strength, but a bit boring in my view. Consider swimming intervals, just as you would when running - 400m warm up, interval session, 400m warm down. Alternatively go for, say, a 1500m to 2000m medium paced effort in place of a 5m run as a rough guide
Hope this helps
Gavin