I lack gold and often only end up with 7-9 trade routes even with Merchant republic
You are talking fast victory... excess gold is wasteful initially...but later for science, sure. Feeling the pinch a bit is OK as long as you get by. A couple of key things on gold and CH
Build 3 early for the trade route eureka and 2 markets for that eureka and the gold does help. Leave the rest until you have your campuses down. You should not be growing cities for more districts but any that can fit a CH after campus, its the best choice.
The main source of gold early is from conflict.... for example smash Tomyris but do not take her out if there is a nearby civ to attack, instead take all he gold off her and then come back later to finish her off... pillage every district you can, the raid card is great for this.. Gilga is a good example for science... he loves science and grows fast, you do not really want to take him out... just every now and then pillage his lands, 50 science per zig with the raid card, 100 gold per horse.
Another source often forgotten is trade, if someone denounces you they will give you ad deals but otherwise the deals will be good so take them as soon as possible, as much as possible.... even allowing your cities to get a little unhappy for gold is OK in my book... -5% in 4 cities may seem a lot but normally its not that bad.
A key one some people use is to place a farm in a breathtaking square in a city. Every city has a farm. Then when 50 gold per appeal point card comes up for swapping farms with neighbourhoods, blow the farm away with a neighbourhood and you get the money immediately, no need to finish building the useless thing. Others use it, why don't you?.... look at lily_lancers finishes in GOTM, every city has a neighbourhood being built.
7-9 routes at the end is OK as long as you have great zim... but ideally the more the merrier for the endgame.
I suffer more from lack of culture at he beginning and am amazed how much some players can get.