K so just a bit more information I personally noticed.
1) Researching takes a LONG time - and it seems to scale depending on how many times you've researched on A SPECIFIC ITEM
For example, I researched a trait on some light chest armor, took 6hs (if i remember correctly) the first time. Next time on light chest armor it took 12 hours (again, if i remember correctly)
For light armor boots - the first research took 6 hrs, and i imagine the second would take 12
Now, does this continually double, or does it cap at some point (maybe 24 hours? I DON'T KNOW
But IMO it's not worth it to put skillpoints into the 'research 2 things at once and faster" because eventually you will have researched EVERYTHING and why waste money on that respec?
2) There are special 'set' crafting tables out in the world - and these ALL require that you have researched THAT SPECIFIC ITEM twice (the least I saw was twice, it might be more later-in-game)
So for example, there was a set that could make me do a knock-back area thing when I fell below a certain amount of health (once every like 3 minutes)
I needed 3 parts of this set for it to 'work'
Each PART (be it a weapon, shield, or armor) required me to have researched 2 traits in each part
So if I wanted to make light chest armor, light armor boots and a restoration staff, I would need to have researched 2 traits in light chest armor, 2 traits in light armor boots, and 2 traits in the restoration staff.
3) I found provisioning to be SUPER awesome - I had found a blue recipe that only took liver and onions, and it gave me 115 to magicka AND stamina for AN HOUR
After getting the skill that makes you make 2(more for later on, but i only got to 2) per 1 set of ingredients I effectively ALWAYS had 115 extra to both of those stats... and I could give them to my group members to make dungeoning easier... really seems like a USEFUL craft to me
As for your questions; the bag space...while super limited - I managed to basically 'do' every craft while actually playing, I just kept my inventory to the bare essentials (some food, some potions and soulgems
And basically hoarded everything 'of importance'
That being said, those [censored] little "carapaces" you can find that say "sell to a merchant" i got rid of and replaced with an actual crafting item
I basically 'deconstructed' all the items I found EXCEPT for the crafting line I KNEW I wouldn't need/use (in the case of my healer, it was the blacksmithing line)
I basically would find tons of heavy armor/weapons and iron ore...I just sold them, and "used" everything else
Got both decent money AND crafting EXP
Naturally you should do this AFTER you sell everything to make a comfortable "starting gold" collection.
And finally;
"How many professions could you feasibly take on at once? I intend to do Clothing for sure, but I'd also like to take Blacksmithing. If I take these two could I also take on some of the "lesser" professions like enchanting, alchemy, or provisioning?"
If I were you I'd just be smart about it - to me it sounds like you are planning on using light/medium armor (hence clothing) and a metal weapon (hence blacksmithing)
You shouldn't waste skill points nor profit from the blacksmithing line - when you could just as easily find someone/pay someone to make you your weapon (if this is indeed your plan)
Likewise, if you were planning on being a heavy armored bow-er, you should go blacksmithing and just pay someone to make you a bow.
It just makes sense to be able to sell one 'main' crafting line for money, and 'do' the one you will use more (naturally armor will always trump weapon, because you can make 6 pieces vs 1 piece)
But to answer your question - yes if you REALLY wanted you could easily do clothing, blacksmithing AND another...it realistically ONLY takes like 5-10 skill points to 'max out the ability to make the highest level stuff' (you don't NEED all of the extra skills like "see ores from 20 feet away")