You've fallen into one basic trap that many, if not most, new players fall into. (And I include myself in this, for I did the exact same thing.) You're trying to build every building in every city. Every one of those buildings is costing you gold every turn, in addition to the time and shields spent building them. It adds up and it adds up quickly. Learn this phrase and learn it well, for you will hear it around here: Your cities do not need anything. The question is: What does your empire need your cities to have?
Rocha. Read this everytime you are about to start a session of civ! The bit in bold; place it on top of the television, have it engraved into your bathroom mirror, commission someone to produce a doormat with it on, print it out and replace any pictures on the walls with this, repeat it three times every day when you get up and when you go to bed. OK, well I might be going slightly over the top but it's great advice, you'll see it given by a number of people but if you follow it you'll be a much better player.
Now for some additional comments:
1. As regards to city placement you seem to be getting the hang of things. This looks so much better than before IMO. With regards to building MoM because there was nothing else to build, build military units everytime. I'll expand upon this point in a minute.
2. Building the FP OTOH was not a bad thing at all. In fact it was a great move! Just don't build it because you've got nothing else to do. I think that I said this before but it reduces corruption in all cities so build it as soon as possible. 200 shields is great value for this small wonder. Note that this is one of the reasons why your corruption is lower than when you played the other games. This is absolutely nothing to do with playing as the Celts. The civs that are commercial will give you lower corruption. Now probably my favourite civ (if I actually have one) is the Iroquois. Their UU is a 3 point attack horse, they are commertial and agricultural. Once you are ready for another change, try these guys out!
3. The reason why I suggested the Celts were that the UU is just the same as the Ancient Cavs you like but it was a way of tempting you into playing a civ that was Agricultural.
If that second bit was a little devious then I'm sorry but 'all's well that ends well'. Note that the main advantages that you have as the celts, apart from a great UU, are +1 food per city (i.e. greater growth), cheaper 'ducts (i.e. greater growth potential), cheaper temples/caths and minimal anarchy. The first two are due to the AGR trait and are much more useful IMO that the ones for REL.
4. You are trying to keep tabs on your cash in some ways but not in others. You are worried about your research capacity but you'd rather keep the lux slider higher than it need to be rather than spending that extra cash on reserch. You are worried about your unit upkeep but you are not worried about city maintenance. I find this very strange. You are happy to build granaries in every town but you are not happy to build another knight in a great town with a rax. Please read the quote at the top of the page again before reading on...
Have you
actually read it again?
As long as you have read it again I'll continue.
If you build something that you don't need, it will cost you money and for no good reason. You don't need granaries in every city and yet they are costing you money every turn. (Build them in a couple of food rich towns when expanding to help pump those cities out but no more). Military units are a different matter. They may cost you money but if you build a few stacks of them, you then go a grab a few cities from a rival civ thus improving your unit allowance and thus you can build more units to grab more cities and so the cycle repeats and you end up owning the whole continent. Consider unit costs an investment for the future.
What to do next
Consider the following points.
From a quick look at the game I would prepare for war with the Vikings by placing my units in attack/defence positions asap. Meanwhile all those useless builds would be converted to knights AND DON'T STOP BUILDING UNITS 'cos when you've finished with the Vikings you are going to take on your other major rival, aren't you?!
I'd make Bodo my first target, not because of the ivory (although its a nice incentive) but because it has their only (known) source of salt.
Worried about cash? Consider this trade:
I'd think twice about trading a 'modern' strategic resource to anyone but do it when I think that it's safe. In this case they are on a different continent and are not the runaway civ so I think that this a wise trade. I'm sure that you'll be keen to take their money-I would be! Also consider further map trades once you have the French WM. This should help you determine whether the vikings have a second source of salt.
Worried about tech progress? Well don't be too concerned as the Vikings will be on their knees soon and will be happy to give you every tech they know for you to leave them alone but if you want Chemistry now, consider this:
Giving luxes to a large civ can be dangerous but I think that you've ensured that they will never be considered 'large'.
Watch out for Viking beserks. Their UU replaces the longbow with a 6 attack point unit that can attack land units from boats. This means that you capital is at risk. Luckily the AI is not very good at using these units and they are expensive but be very wary of any viking galleys heading towards your coastal cities.
Good Luck!
ps re the business about 20 turn deals. Aabra was wise to stop you from breaking that as you will have trashed your trading rep. There is an article in the War Acadamy on this so take a look. It doesn't mention breaking PTs in there IIRC but they are the same as any 20 turn deal. If you are the one that breaks a 20 turn deal, your trading options are severly restricted for the remainder of the game. (Neither of the two deals above would have been possible) I'll keep it at that as the article explains it really well IMO but please post any questions if you wish.
pps have you downloaded
CivAssistII or
MapStat yet? Either one of these will help you stop riots and thus stop you from overcompensating on the lux slider.