Would this type of workout be appropriate if I just finished building up mileage and have only been holding it for 3 weeks? Or should I stick to another workout for now? Thanks
it depends how long-term you are prepared to plan.
if you're looking for a quick fix for a 5km race in two months, then that 20 x 200m session you describe is almost as good as anything else, considering that you've only just started running tempos. hold your mileage until around 3 - 4 weeks before the race, then reduce it by around 15 - 20% each week. race. rest. base. repeat.
but if you are looking for long-term development as an athlete, I would adopt a different approach.
1. start with some low key strides over short distances. you can do this on grass, on a sports field or golf course or something of that nature. you want short efforts (up to 1 min in duration) where you don't worry about speed but concentrate on looking like an athlete. I tell my lads to imagine they are on tv and their mum is watching and they have to look good for as long as the camera is pointed at them. then slow down and jog easy for a couple of minutes until you feel ready, then go again. do around 4 - 6 of these per session. warm-up, cool down, around 5 miles total.
2. when you have been doing 1. above for 3 - 4 weeks, start adding some simple running drills into your warm-up. the main point of these drills is to reinforce neuro-muscular pathways, so you will need to do them briefly, regularly, forever. shorten the repeats but increase the pace a little. get up on your toes and think about being a miler. don't worry about the actual speed but try to think very deliberately about how feet and hands co-ordinate to control speed. keep it at 4 - 6 repeats, take as much recovery as you need. warm-up, cool down, around 5 miles total.
3. when you have been doing 2. above for 3 - 4 weeks, after your warm up and running drills, change into your road racing shoes. you should still be on grass, but if you prefer you can do this on tarmac, or even on a track but not yet in spikes. if you have no racing flats, then your regular training shoes will do. the point here is that we are transitioning to doing highly intensive track work in spikes, so this stage should be an intermediate between what you have been doing and what you want to do. keep the repeats fairly short around 100m, and don't start too fast, around your best 800m pace. run 4 - 6 of these, and as you work through the set try to increase the pace just a little so the last one is around your 400m pace. over the following 4 weeks or so, gradually shorten and sharpen the repeats each week so that you end up running 6 x 50m at 400m pace with a long slow walk back recovery.
over the 8 - 10 weeks that this has taken you, you will notice a significant increase in your basic speed, a significant increase in your awareness of and control of your pace, and you will have developed both the neuro-muscular systems and the muscle recruitment protocols to prepare you for doing some more serious workouts, injury-free.
as you mature as an athlete, this set of 6 x 50m sprints will become part of your warm-up for a more extended track session, and you can add other things on top as the situation requires. a sample would be to do this, then jog a lap to recover, then do 8 - 10 x 200m at 800m pace, with a 2:00 walk to recover. but you need to build up to this, you can't just jump in here, not at 65 mpw, without doing the preparation.
at this point the tempos you have been running can start to morph into something a bit more specific for your event, so your two workouts each week can be this speed session, and a second session of longer intervals at a pace appropriate to your goals.
cheers.