Well, sort of. It's certainly possible to start off with mercenaries, and do well, but the problem is that Mercenaries army selection is very different from other factions. Because I answered this question a little while ago, I'll do a bit of a copy and paste from that post:
Mercenaries is a bit of an odd-ball for a faction - it handles like 4 mini-factions in the same faction, and that makes for some very tight restrictions on what units you can have in a particular list.
The four mini-factions are Searforge (Rhulic dwarves), Talion (Pirates Arr!), High-Born Covenant (resistance fighters from Llael), and Four Star (The most generic mercenaries faction). Some models are only usable for a particular mini-faction, some work for a few. Usually you'll find Rhulics and Pirates are very restricted, but most of the models will generally also work for either High-Born or Four Star, as they're more diverse groups. For instance, Durgen Madhammer is a Rhulic Dwarf warcaster, but he'll work for Highborn or 4 star as well as Searforge. Then again, his own rules only allow him to take Rhulic jacks, even if you take him in a 4* list, which further restricts his choices.
Each caster also has their own Theme list they can take, which sometimes allows for very different sets of units to be taken. For instance, Magnus the warlord (a cygnarian Traitor) has a theme list called the bad-seeds, which allows him to take a certain number of Cygnarian units (basically defectors).
So basically, list selection is a little harder, but mercenaries as a faction is certainly fun and viable.
Both high-born and 4Star have access to some rhulic and pirate units, so they might be good factions to start planning with. You can read a bit more about them, and find out what models work for which factions by looking up Battle Collage
- a great reference site. The mercenary book also lists them, though I find Battle Collages layout easier to flip between to see everything.
Personally, if you like the look of mercenaries, I'd go for them. Plus, if you take up another faction later on, you have mercenaries to use with them