Re: small bathroom configuration
You're kidding, right? You want to shoehorn all that into a space of just 3 feet wide and 8 feet long? A typical 1/2 bath or full bath is at minimum 5 feet wide to accommodate a tub or a toilet/sink within it's width.
Aside from fitting the fixtures into the space, you've also got to have plenty of room to use each device without feeling claustrophobic, which you would in your scenario. Lastly, in the case of the toilet, you need a minimum of a 3 foot square just for the toilet, you need another 2 feet in front of it to be able to comfortably sit down without scraping your face down the wall as you do so.
So, in answer to your question, no, you cannot put all that into the space you're suggesting. The only way I can see it working is if you were to salvage a toilet/shower from an RV where the toilet and shower are molded into the same unit, but then you introduce a whole new set of problems, mechanical, physical, and aesthetic.
Now, if you were willing to extend the porch to accommodate the space needed for a comfortable, usable bathroom, then it's absolutely do-able.
I suffer from CDO ... Its like OCD, but in alphabetical order, LIKE IT SHOULD BE!!!