What jacket? Help please...

Personally I'd try and avoid anything totally waterproof with a membrane if you're going to be doing a decent workrate. Even the best (and Event is the best I've used by a long way, haven't tried the new generation of Gore fabrics though) will get you hot.
Wherever possible just go windproof and stick some layers on underneath. Save the waterproofs for when it's really tipping it down (not as often as you'd think) and you'll be much more comfortable.
And for windproofs I'd personally go for something woven (e.g. Pertex type fabric) if possible rather than a membrane (e.g. Gore Windstopper- again though things might have moved on since I got mine).

Of course YMMV on all of this. I frequently see people riding around happily (I assume!) in outfits that would make me melt after 500m.

Here are my thoughts on breathable versus fully waterproof Stephen. You could of course say I'm biased, but I could choose any solution or fabric and chose this, so its all thought out:
http://www.vulpine.cc/Blog/bikes-tech/choosing-the-best-possible-rain-fa...

Any waterproof top will make you more likely to sweat if you are working at all hard, I have a Specialized one made from Goretex Active Shell (the most breathable of their waterproof fabrics) and I still get the boil in the bag sensation when pushing on. I'd suggest you need different tops for when it's raining and when it isn't.

When it's dry go for a top with a windproof front and breathable back and then just stick on as many merino layers as needed underneath to keep you warm for the temperature that day. Planet X do merino tops for not too much money, their winter bundle has a long and short sleeve one I think.

If you run hot look for tops with zip vents on the front and under the arms, they make a surprising difference.

Above 10 degrees(ish) in the winter (commuting on a hybrid) I'm normally OK in shorts (baggy shorts over cycle shorts in non-'roadie' mode), Icebreaker merino top (150 or 200) and a waterproof top - Altura night-vision. I can vouch for its durability over 4 years and I recently slid down the road in it after coming off. I'd quite like the more pricey Gore Bike Wear versions but the Altura just won't die! The only places that I need really 'toasty' kit are fingers and toes (just use thick hiking socks). Sub 10 degrees and I chuck some tights over the padded shorts. On the road bike I just ditch the baggy shorts and if I think I might get a bit warm, I just layer up (baselayer, cycle top, gilet, arm warmers) and keep a lightweight 'tea bag' style waterproof in one of my pockets). Snag I find with some of the waterproof tops is they don't roll up very small if you want to shed them.

I have a Gore softshell and I wouldn't be without it. Over shoes will work with trainers but your trainers are likely to be bulkier than cycling shoes so buy at least one size up if not two. Only use the overshoes on rainy days, you will wear through the toes pretty quicky if you use them for commuting every day. If you have a set of long mudguards you will only need overshoes if it is really tipping down.

If I were you I would get a Nightvision jacket - bright yellow - for commuting there isnt much to touch it. That's what I started out in. I now commute in a Gabba and Sportful No Rain bibs.

Just remember, if you are cold and wet you wont stick at it, but its pointless spending loads on kit when it wont fit you in 6 months - the weight flys off

Cost is high but it is well worth the investment.

Castelli Gabba ss with nano flex or no rain arm warmers. The gabba has basically replaced every other piece of wet / winter weather kit I have.

For 8.5 miles you can just wear what ever makes you comfortable and it doesn't *need* to be cycling specific.
My personal choice would be for a windproof softshell and a base layer with a cheap pack away non breathing waterproof and some water proof gloves for when it is really chucking it down. You can probably get away with shorts as your ride isn't that far but riding for long periods with your knees and ankles uncovered in the cold can lead to injury so you might like to consider some tights.
You will get sweaty in a waterproof whatever it is, it is just a matter of choice warm and sweaty or soaked in rainwater and cold. You might find in summer that you prefer not to wear anything water proof on your commute but in the winter, sweaty is probably the lesser of two evils. Water proof trousers will stop rain running into your shoes too. Are you riding in cycling shoes or trainers?

I for years used to use a basic altura waterproof which was not breathable. It is ok but sweaty. I recently switched to a dhb soft shell and really like it - kept me dry and toasty in last night's rain. There are two vent pockets at the front for breathability. I can't see myself using anything else. Gore is great but expensive.

I cycle a simlar distance and have done for ten years, you'll not be riding long anough to get that wet/cold mate. If I were you get a packable windproof (I've got a gore Xenon II).

As for your legs, a cheapish pair of longs preferable with reflective patches is best. Most important if you wish to continue commuting through January and February is a buff/skull cap/gloves and overshoes. Without those you'll suffer, I recommend a planet X bundle if funds are limited.

And by the way, I usually wear only shorts until Christmas, trust me it gets a hell of a lot colder yet.

Spotted some builders with hi viz hoodies / reflective panels. Picked one up in Aldi for about £12. You can pick them up on Ebay for under £20, and for commuting and general utility riding, they're the dogs'. Warm, and very visible.

I use a gortex waterproof yellow jacket with no insulation.
Keeps wind and rain out.
In summer just cycle top under if using jacket at all.
Winter add base layers or fleece.

Use Lycra bib/braces, plenty warm enough with lower back protection in winter, shorts under for padding and in case sun comes out.

Carry waterproof gortex over trouses in case of heavy rain.

I wear waterproof breathable shimano Mp spd boots ( can walk, tread above spd cleat) all year round.

Hope this helps?