I am thinking about visiting Crete for 4-5 days in early to mid-October. I would then go to Italy for a week or so after that.

What can I expect the weather to be like on Crete? How likely is it to be rainy? I am planning on outdoor activities for most of those days.

No one can answer your question today or tomorrow or next week.
Couldn't you try doing a search "Crete Weather" and you'll find a wealth of historical data.
This gives you the range of weather and temperatures from 2014. You can go back many years if you want.

I've lived in Crete for the last ~30 years and as UAPremExecflyer wrote, one can't answer the question. It's usually warm and pleasant (a little cooler after sunset) but you could have a bad storm with rain and wind or, more seldom that part of the year, strong south winds with very hot weather. Even if I said that you have a 80-90% probability of fine weather, you may go there to find out that you chose the 10-20%...

Thanks! That's what I was looking for. 80-90% is pretty good odds of pleasant weather.

Crete is further south, and not plagued with the wind condition problems the Cyclades(Mykonos, Santorini, etc.)have during the fall and winter seasons.

I fully agree with the assessment from KLouis. But just to add a bit, even if you hit bad weather on Crete, from my own experience living on the island, it is often easy to escape it in Autumn or Spring. Due to the geography of the island, with a mountain chain running along the spine from the west to the east, you will often find the winds from the north that are most likely to bring the rains. If this happens, chances are quite big the plains among the northern part of the island (where the vast majority of people live) will have rain, but when you travel to the southern coast across the mountains, you can easily find blue skies and sunny weather when at the other side. Keep this in mind when being based in the north and visiting places on the southern coast like Preveli, Paleochora, Sfakia, Loutro etc.

It is plagued with exactly the same wind condition problems. But Crete being bigger (the latitude will even make it worse!), you can often find ways to avoid it (see Romanianflyer's answer).

Due to work projects, I am now thinking about Crete first week of November. Looks like a better chance of rain? Temps still look ok, maybe even better - I tend to like it a little cooler.

Rather than a 80-90% chance of good weather, now look at a value of 60-70%. You can also swim on those days: I can stay in the water for ~15-20 min., but my wife who's German can stay for much longer. Added advantages in November: if it rained a couple of times in October, the island will be covered by a green "carpet" and you could drink "nouveau" wine and eat winter goodies.