I'm mainly a guitar player, but sometimes I also pick up my 4-string instrument. The exact model is Yamaha RBX-170. It has PJ pickup configuration, which means that it has a p-bass pickup in the middle and jazz-bass pickup near the bridge. As an amp I used to use the Hartke Kickback-12, but as it was too big and heavy I have considered getting something smaller and portable for a long time. In the fall I will probably order myself a TC-Electronic bh250 for a head and bc208 from the same company as a cab. Acording to the reviews the head is really small, so you can easyly stick it into your gigbag. It also has some nice chorus, octaver and compressor effects. In order to change the effects you have to use the Toneprint app on your smartphone, but I've tested it and it is completely usable on Android. Also, the head has class-d poweramp, so if you don't want to use the cab and want to connect it straight to the mixer or audio interface, you can do it via the xlr output.
The 2x8 cab doesn't have so much bottom end as the larger ones, but it is a lot more portable and I can probably drag it much more easily to some jam sessions. Also as a drive pedal I'm planning to buy the Electro Harmonix bass soulfood. In addition to some nice drive sounds it has also the blend knob, so you can mix your dirty sound with the clean sound.

I have an ibanez 5 string with active pickups in it.  Sounds very nice.    I don't use an amp, for I just use a VST to run my sounds, but if I had to get an amp, i"d probably get the aluminum cone speaker Hartkey cabs.  I'm a fan of Victor Wooten.

Yes, especially when there is so much slack in the string while being tuned so low. In fact when pressing too hard on the string in standard tuning, the pitch still goes upp a little bit. So that's why you have to apply just enough pressure and not too much. Here is one guy demonstrating it:
https://www.youtube.com/watch?v=ZGNsAU3Mv_k

Upright Basses. Those are used in Jazz for walking Bass lines just like a Bass Guitar. But they shine best in the Classical Family. In that family consists of: Violin, Viola, Cello, and Upright Bass.

I almost went for a Seven String , but then I settled for the Ibanez 6-String. I had a ESP LDTb55 5-String with 24-Jumbo Frets but I gave it to a friend of mine because he had the Electric Guitar that he set up for me just for free. I did like ESP Basses, but can't seem to find one similar to the ESP LTDB55 Model. At the time it was $240, and I bought a case for it for $40. So it was $280 plus $3 in tax.