I'll start by saying - if you enjoy RTS games just buy it since there is more S in here than in 5 other games put together so just go for it...

Regarding SP - although, as you know, there is no campaign or story, there are loads of maps ranging from single solar system with handful of planets to huge ones that might take you day or two to complete... All this is backed up with simple yet rather well designed achievement system broken into dozen upon dozen bits that you should go through before reaching 100% (to give you an idea - i have been playing this game for months and am still no where near of reaching 100% achievement) So yes, there is plenty things to do in here... AI is exceptionally good too and it will keep you be busy for quite some time

Regarding your question on fleet management - it is genius! Simple as that really... You will pick it up very quickly and control dozens (hundreds!?) of ships in no time

Real gem, however, is in playing online vs human opponents - this part of the game is arguably the only one where developers are not reaching and delivering full potential of Sins... Yes, it is very good as is, but there are fair few 'holes' to put it simply which are preventing this game to truly shine online hence rather small online community.

Hope this helps

Not a problem.

First question:

Many of these colonization/expansion games don't have a 'campaign' mode, but that hasn't stopped many people from putting in tons of hours into them - Civilization, SimCity, etc. There was no story to MOO2 either, but I certainly put in a good number of single-player hours. There are numerous situations, tactics, and team compositions to try. You can also 'unlock' teams to build and break alliances as you see fit.

And despite being mostly a single-player guy, you might just like the multiplayer. It's awesome for LANs.

Second question:

Fleet management is something new compared to Homeworld or Starcraft - it's sort of like a hotkey group that can automatically grow when reinforcements arrive. It makes your life easier.

Traditional:

1. Make units, make hotkey.
2. Go kill something, lose units.
3. Make more units, move units to old group.
4. Select all units, remake hotkey.

Sins:

1. Make units, make fleet.
2. Go kill something, lose units.
3. Make more units, move units to old group.

Most of the time, people skip step 3 by making setting the rally point to the fleet. If you find that you don't like it, traditional hotkeys are still available.

Yup, good choice.

The lack of experience in playing 4X games won't matter really, because imo Sins is really not a "4x" game although advertised (and having gained status) as such. To me it really seems more of a slow paced and large RTS combined with a touch of simcity.

Single player sucks imo. It was kinda fun at first...but the AI is just too bad when your skills improve. This game is definetely at its best online (as RTS games usually are). See you there