1. What is an omnidirectional antenna?

Type of antenna which receives or transmits signals in all directions along one plane with equal strength. Thank to that you can recive signal from whenever you are in particular area. Omnidirectioanl antenna radiation pattern:

IPXY is an Ingress Protection Rating, which defines protection levels of certain product. X from 0-6 defines security level from penetration of solids. Y from 0-9 defines security level from water.

3. Why placing router and antenna in one enclosure is better?

The biggest benefit of router and antenna being next to each other is the reduction of cable used to connect the elements. Reducing the cable length reduces its loss, which has high impact on signal quality.

Porównaj

Antenna QuSpot for MikroTik RBM11G | LTE

P/n: AMT11LS

Integrated multi-band LTE omni antenna + place to install MikroTik RBM11G (All-in-one)

QuSpot omnidirectional LTE 2x2 MIMO antenna for MikroTik RBM11G is a perfect outdoor device for mobile and fixed installations like CCTV, hotspots, industrial areas, campervans, ships etc. The set contains IP67 ABS enclosure, LTE antennas, RJ45 (Ethernet) port and mast/pole/wall mounting bracket.

If you use RBM11G with QuSpot antenna, you get an integrated complete solution with embedded router and multi band antennas in one enclosure.